Hitler's U-boat war.

by Clay Blair.

FOREWORD.

On a chilly day in the late fall of 1945, our submarine, the U.S.S. Guardfish, proudly flying battle pennants, nosed into the Submarine Base, New London, Connecticut, joining scores of mass-produced sister ships, all "home from the sea."

Collectively we submariners were known as the "Silent Service," and proud we were of that distinction. Unknown to the public, we had played a decisive role in the defeat of Japan. In forty-two months of secret warfare in the Pacific Ocean area, 250 of our submarines, mounting 1,682 war patrols, had savaged Japanese maritime assets, sinking 1,314 ships of 5.3 million gross tons, including twenty major warships: eight aircraft carriers, a battleship, and eleven cruisers. For almost three years Guardfish Guardfish, a fine boat, had played a prominent role in that war, sending nineteen confirmed ships to the bottom (including two fleet destroyers and a patrol boat) during twelve long and arduous war patrols in Japanese-controlled waters.

After we had moored at a pier where we were to "mothball" Guardfish Guardfish, we were startled to see a strangely different submarine close by. Painted jet black, she looked exceptionally sleek and sinister. We soon learned that she was a German U-boat that had surrendered shortly after VE-Day. She was manned by an American crew that was evaluating her on behalf of naval authorities in Washington.

This U-boat was very hush-hush and off-limits to ordinary souls. However, when she shifted her berth to "our" pier (and nicked us in the process), we became friendly with the American crew and gradually talked our way on board for a look-see. We learned that she was U-2513 U-2513, a brand new Type XXI "electro boat," one of two such craft allotted to the U.S. Navy as war prizes. Commissioned and commanded by one of Germany's most famous U-boat "aces," Erich Topp, she and her mass-produced sister ships had been completed too late to participate in the war.

In our superficial examination of U-2513 U-2513, we were quite impressed with some of her features, especially her top speed submerged. She had six sets of storage batteries, comprising a total of 372 cells (hence "electro boat"), which enabled her to quietly sprint submerged at about 16 knots for about one hour. This was twice the sprint speed of our submarines and sufficient to escape from almost any existing antisubmarine warship. Alternately, the large battery capacity enabled her to cruise submerged at slower speeds for a great many hours, whether stalking prey or escaping.

The next most impressive feature to us was her Schnorchel Schnorchel, or as we anglicized the German, snorkel. This was a sophisticated "breathing tube" or mast with air intake and exhaust ducts, which enabled U-2513 U-2513 to run her two diesel engines while submerged. By rigging one diesel (or both) to charge the batteries while submerged, she could in theory remain underwater for prolonged periods, thereby greatly diminishing the chances of detection by enemy eyes or radar. to run her two diesel engines while submerged. By rigging one diesel (or both) to charge the batteries while submerged, she could in theory remain underwater for prolonged periods, thereby greatly diminishing the chances of detection by enemy eyes or radar.

Nor was that all. Her periscope optics and passive sonar for underwater looking and listening were much superior to ours. Her ingenious hydraulically operated torpedo-handling gear could automatically reload her six bow torpedo tubes in merely five minutes. A third reload could be accomplished in another twenty minutes. The thickness and strength of her pressure hull was said to give her a safe diving depth limit of about 1,200 feet, twice our safe depth limit and sufficient to get well beneath most existing Allied depth charges. She even had an "automatic pilot" for precise depth-keeping at high speeds.

Much later, when some of these details and others about the Type XXI "electro boat" leaked out, they caused an utter sensation in naval circles. Prominent experts gushed that the Type XXI represented a giant leap in submarine technology, bringing mankind very close to a "true submersible." Some naval historians asserted that if the Germans had produced the Type XXI submarine one year earlier they almost certainly could have won the "Battle of the Atlantic" and thereby indefinitely delayed Overlord, the Allied invasion of Occupied France.

The American evaluators on U-2513 U-2513 were not so sure about these claims. In the classified report they sent to the Chief of Naval Operations, dated July 1946, they wrote that while the Type XXI had many, desirable features that should be exploited (big battery, snorkel, streamlining, etc.), it also had many grave design and manufacturing faults. The clear implication was that owing to these faults, the XXI could not have made a big difference in the Battle of the Atlantic. Among the major faults the Americans enumerated: were not so sure about these claims. In the classified report they sent to the Chief of Naval Operations, dated July 1946, they wrote that while the Type XXI had many, desirable features that should be exploited (big battery, snorkel, streamlining, etc.), it also had many grave design and manufacturing faults. The clear implication was that owing to these faults, the XXI could not have made a big difference in the Battle of the Atlantic. Among the major faults the Americans enumerated: * POOR S STRUCTURAL I INTEGRITY. Hurriedly prefabricated in thirty-two different factories that had little or no experience in submarine building, the eight major hull sections of the Type XXI were crudely made and did not fit together properly. Therefore the pressure hull was weak and not capable of withstanding sea pressure at great depths or the explosions of close depth charges. The Germans reported that in their structural tests the hull failed at a simulated depth of 900 feet. The British reported failure at 800 feet, less than the failure depth of the conventional German U-boats.

* UNDERPOWERED D DIESEL E ENGINES. The new model, six-cylinder diesels were fitted with superchargers to generate the required horsepower. The system was so poorly designed and manufactured that the superchargers could not be used. This failure reduced the generated horsepower by almost half: from 2,000 to 1,200, leaving the Type XXI ruinously underpowered. Consequently, the maximum surface speed was only 15.6 knots, less than any oceangoing U-boat built during the war and slightly slower than the corvette convoy-escort vessel. The reduction in horsepower also substantially increased the time required to carry out a full battery charge.

* IMPRACTICAL H HYDRAULIC S SYSTEM. The main lines, accumulators, cylinders, and pistons of the hydraulic gear for operating the diving planes, rudders, torpedo tube outer doors, and antiaircraft gun turrets on the bridge were too complex and delicate and located outside outside the pressure hull. This gear was therefore subject to saltwater leakage, corrosion, and enemy weaponry. It could not be repaired from inside the pressure hull. the pressure hull. This gear was therefore subject to saltwater leakage, corrosion, and enemy weaponry. It could not be repaired from inside the pressure hull.

* IMPERFECT AND H HAZARDOUS S SNORKEL. Even in moderate seas the mast dunked often, automatically closing the air intake and exhaust ports. Even so, salt water poured into the ship's bilges and had to be discharged overboard continuously with noisy pumps. Moreover, during these shutdowns, the diesels dangerously sucked air from inside the boat and deadly exhaust gas (carbon monoxide) backed up, causing not only headaches and eye discomfort but also serious respiratory illnesses. Snorkeling in the Type XXI was therefore a nightmarish experience, to be minimized to the greatest extent possible.

The U.S. Navy did in fact adopt some of the features of the Type XXI "electro boat" for its new submarine designs in the immediate postwar years. However, by that time the Navy was firmly committed to the development of a nuclear-powered submarine, a "true, submersible" that did not depend on batteries or snorkels for propulsion and concealment. These marvels of science and engineering, which came along in the 1950s, 1960s, and later, were so technically sophisticated as to render the best ideas of German submarine technology hopelessly archaic and to assure the United States of a commanding lead in this field well into the next century.

This little story about the Type XXI "electro boat" is a perfect example of a curious naval mythology that has arisen in this century. The myth goes something like this: The Germans invented the submarine (or U-boat) and have consistently built the best submarines in the world. Endowed with a canny gift for exploiting this mar-velously complex and lethal weapon system, valorous (or, alternately, murderous) German submariners dominated the seas in both world wars and very nearly defeated the Allies in each case. In a perceptive study,* Canadian naval historian Michael L. Hadley writes: "During both wars and during the inter-war years as well, the U-boat was mythologized more than any other weapon of war." Canadian naval historian Michael L. Hadley writes: "During both wars and during the inter-war years as well, the U-boat was mythologized more than any other weapon of war."

The myth assumed an especially formidable aspect in World War II and after-wards. During the war, the well-oiled propaganda machinery of the Third Reich glorified and exaggerated the "successes" of German submariners to a fare-thee-well in the various Axis media. At the same time, Allied propagandists found it advantageous to exaggerate the peril of the U-boats for various reasons. The end result was a wildly distorted picture of the so-called Battle of the Atlantic.

After the war, Washington, London, and Ottawa clamped a tight embargo on the captured German U-boat records to conceal the secrets of codebreaking, which had played an important role in the Battle of the Atlantic. As a result, the first "histories" of the U-boat war were produced by Third Reich propagandists such as Wolfgang Frank, Hans Jochem Brennecke, and Harald Busch, and by Karl Donitz, wartime commander of the U-boat force, later commander of the Kriegsmarine Kriegsmarine, and, finally, Hitler's successor as Fuhrer Fuhrer of the Third Reich. These "histories," of course, did nothing to diminish the mythology. Hampered by the security embargo on the U-boat and codebreaking records and by an apparent unfamiliarity with the technology and the tactical limitations of submarines, the official and semiofficial Allied naval historians, Stephen Wentworth Roskill and Samuel Eliot Morison, were unable or unwilling to write authoritatively about German U-boats in the Battle of the Atlantic. Hence for decade after decade no complete and reliable history of the Battle of the Atlantic appeared, and the German mythology prevailed. of the Third Reich. These "histories," of course, did nothing to diminish the mythology. Hampered by the security embargo on the U-boat and codebreaking records and by an apparent unfamiliarity with the technology and the tactical limitations of submarines, the official and semiofficial Allied naval historians, Stephen Wentworth Roskill and Samuel Eliot Morison, were unable or unwilling to write authoritatively about German U-boats in the Battle of the Atlantic. Hence for decade after decade no complete and reliable history of the Battle of the Atlantic appeared, and the German mythology prevailed.

My wartime service on Guardfish Guardfish kindled a deep and abiding interest in submarine warfare. As a Washington-based journalist with kindled a deep and abiding interest in submarine warfare. As a Washington-based journalist with Time, Life Time, Life, and the Saturday Evening Post Saturday Evening Post, I kept abreast of American submarine developments during the postwar years, riding the new boats at sea, compiling accounts of the noteworthy advancements-and politics-in articles and books.* In 1975 I published a work of love, In 1975 I published a work of love, Silent Victory: The U.S. Submarine War Against Japan Silent Victory: The U.S. Submarine War Against Japan, the first, full, un-censored history of the "Silent Service" in that very secret war.

The publication of Silent Victory Silent Victory triggered suggestions that I undertake a similar history of the German U-boat war. However, owing to the embargo on the U-boat and codebreaking records, still in force after thirty years, this was not possible at that time, but the idea took root. While I was engaged in other military histories over the next dozen years, Washington, London, and Ottawa gradually released the U-boat and codebreaking records. During the same period German naval scholars, notably Jurgen Rohwer, mined the German U-boat records and produced quite valuable and objective technical studies and accounts of some combat actions and related matters. triggered suggestions that I undertake a similar history of the German U-boat war. However, owing to the embargo on the U-boat and codebreaking records, still in force after thirty years, this was not possible at that time, but the idea took root. While I was engaged in other military histories over the next dozen years, Washington, London, and Ottawa gradually released the U-boat and codebreaking records. During the same period German naval scholars, notably Jurgen Rohwer, mined the German U-boat records and produced quite valuable and objective technical studies and accounts of some combat actions and related matters.

By 1987 I was able to undertake a U-boat history. Happily, Random House shared my enthusiasm for the project and provided the necessary financial resources. My wife, Joan, and I camped in Washington, London, and Germany for many months, culling and copying tens of thousands of pages of documents and microfilms at various military archives and collecting published works on the Battle of the Atlantic and codebreaking. While in Germany we made contact with the U-boat Veterans association and interviewed former U-boat force commanders, skippers, and crewmen. Subsequently we kept abreast of the spate of scholarly and popular U-boat books and articles about phases or aspects of the war that appeared in the late 1980s and 1990s, much of it first-rate.*

The result of this research is this new and complete history, which, owing to its length, is published in two volumes. I view the U-boat war quite differently from other historians and popular writers. As I see it, there were three separate and distinct phases: the U-boat war against the British Empire, the U-boat war against the Americas, and the U-boat war against both the British Empire and the Americas. Together with an introductory section, "Background for War," the first two phases of the war are dealt with in this volume, The Hunters The Hunters; the third phase in Volume II, The Hunted The Hunted. Each volume contains appropriate maps, photos, plates, appendices, and an index.

As the reader has doubtless concluded, my assessment of the U-boat peril-and war-is also quite different from that of most other historians and popular writers. In a word, the U-boat peril in World War II was and has been vastly overblown: threat inflation on a classically grand scale. The Germans were not supermen; the U-boats and torpedoes were not technical marvels but rather inferior craft and weapons unsuited for the Battle of the Atlantic. In contrast to the strategic success of our submarine force versus Japan, the German force failed versus the Allies in the Atlantic. The main contribution the U-boat force made in the war was to present a terror weapon, a sort of "threat in being," which forced the Allies to convoy, delaying the arrival of goods and supplies, and to deploy extensive antisubmarine counterforces. The myths notwithstanding, only a tiny percentage of Allied merchant ships actually fell victim to U-boats. Ninety-nine percent of all Allied merchant ships in the transatlantic convoys reached assigned destinations.

This is not to say that the Battle of the Atlantic was a cakewalk for the Allies, or for that matter, an easy threat for the Germans to mount. On the contrary, it was a bitter, painful struggle for both sides, the most prolonged and arduous naval campaign in all history. It deserves a history by one familiar with submarines of that era, with access to all the official records, uninfluenced by propaganda and stripped of mythology.

CLAY B BLAIRWashington, D.C., London, Hamburg, and Washington Island, Wisconsin 1987-1996.

* Count Not the Dead: The Popular Image of the German Submarine Count Not the Dead: The Popular Image of the German Submarine (1995). (1995).

* The Atomic Submarine and Admiral Rickover The Atomic Submarine and Admiral Rickover (1954), (1954), Nautilus 90 North Nautilus 90 North (1958), etc. (1958), etc.

* For a list of all sources, see Bibliography. For a list of all sources, see Bibliography.

PROLOGUE.

BACKGROUND FOR WAR.

EARLY D DEVELOPMENTS.

For centuries, militarists recognized that a submarine's invisibility provided it with two distinct advantages: surprise in the attack and the ability to withdraw with impunity. From earliest recorded times, inventors attempted to build combatant submarines. They mastered watertightness and ballasting but could not devise a practical means for propelling the submerged submarine in a controlled direction in the face of tides and currents.

The development of an efficient coal-fired steam engine in the 1800s offered a possible solution to submerged propulsion. Steam could be "stored" under pressure for a limited time. Inventors designed submarines that were to travel on the surface to the combat zone powered by steam engines, then submerge for the attack and withdrawal, powered by stored steam. But steam-powered submarines proved to be less than satisfactory. The engines generated nearly unbearable heat inside the small hulls. The furnaces emitted sooty exhaust that could be seen for miles at sea, robbing the submarine of stealth, one of its chief assets. Moreover, the smokestack had to be disassembled and stored before diving, a cumbersome and time-consuming procedure.

Far better solutions to submerged propulsion became apparent about 1880 with the nearly simultaneous development of the internal combustion engine, the electric motor, and the storage battery. Most inventors designed submarines that were to be powered by gasoline engines on the surface and battery-driven motors while submerged. Others designed submarines powered entirely by battery-driven motors. Still others, combining old and new technology, designed submarines powered by steam engines for surface travel and battery-driven motors for submerged travel. All early versions had drawbacks: Gasoline engines were difficult to start and unreliable in operation, and emitted dangerous fumes. Batteries were bulky, heavy, and weak. Steam engines still generated too much heat.

These propulsion experiments gave promise of a practical submarine. But a breakthrough in weaponry was also needed. The existing weaponry was limited and hazardous: time-fused mines (or bombs), which had to be screwed to the bottom of enemy ships, or spar-mounted contact mines, which had to be rammed against the side of the enemy ship. Both weapons required close-near suicidal-contact with the enemy.

The solution to the weaponry was provided by an English engineer, Robert Whitehead, who lived in Fiume, Austria. In about 1866 he introduced what military historians today would describe as a "stand-off weapon": an automotive or self-propelled mine or torpedo. The Whitehead torpedo was powered by compressed air stored in a large flask. When released, the air turned pistons, which spun a propeller. The first model was primitive: fourteen feet long and fourteen inches in diameter, weighing about 300 pounds. It had a range of 700 yards at 6 knots. The experimental "warhead" in the nose, which was set off by a contact "pistol" when it hit the side of a ship, was puny: eighteen pounds of dynamite. But it worked.

The Whitehead torpedo did not create an immediate sensation in naval circles. But Whitehead soon increased its size, power, range, and the lethality of the warhead. An Austrian, Ludwig Obry, adapted the gyroscope to the torpedo, giving it directional control. With each improvement, naval authorities paid greater interest. Before long the idea took root that Whitehead torpedoes, fired from cheap, small, speedy vessels, might be employed effectively to attack expensive big ships of the line. In due course this concept evolved into the torpedo boat, then into the torpedo-firing destroyer, which were embraced first by weaker naval powers and ultimately by all navies.

The Whitehead torpedo had not been envisioned as a submarine weapon, but by happenstance it was just what submarine proponents had been looking for. With its ability to sneak up on the quarry submerged, unseen and undetected, shoot, then retire submerged with relative impunity, the submarine could be a superior torpedo launcher to the torpedo boat or destroyer.

Soon all submarine designers were recasting plans to incorporate the Whitehead torpedo. This breakthrough stimulated considerable interest among the weaker naval powers, but introduced new levels of complexity. The weapon system required a torpedo tube in the bow of the submarine's pressure hull and a compressed air system for "charging" the torpedo and for booting it from the tube. The tube had to have interlocking inner and outer doors that could be flooded for firing and drained for reloading a second or third projectile. Since the latest torpedoes were very heavy-and getting heavier as the warhead increased in size and lethality-a compensating ballast system had to be devised to offset the sudden loss of weight upon firing and the shifting about of reloads. Otherwise the delicately balanced submarine would go out of control, popping to the surface or plunging to the bottom.

Submarines employed compressed air for blowing main ballast tanks and for other purposes, stored in steel bottles under very high pressure. The incorporation of gasoline and steam engines and battery-powered motors provided the submarine with a power source to operate onboard air compressors. Hence submariners had the equipment and know-how for providing the considerable compressed air required for charging the torpedo flasks and for ejecting the torpedo from the tube.

These technological breakthroughs launched a submarine arms race. By 1890 torpedo-firing submarines utilizing a variety of propulsion systems (all steam; all electric; steam-electric; gas-electric) were under construction worldwide. The stronger naval powers-Great Britain, Germany, the United States-showed little interest in the submarine, but the weaker naval powers-France, Russia, others-embraced it with a passion. Unwilling to compete in the Anglo-German naval race, France became the first nation in the world to place substantial state resources behind submarine development. By 1906 the French navy had nearly ninety submarines in commission or under construction.

Of the submarine designers, an Irish immigrant to the United States, John P. Holland Holland, was the most inventive and able. His boat, Holland Holland, equipped to fire the Whitehead torpedo, was the engineering marvel of the 1890s, superior to all submarines in the world. For surface operations she employed a four-cylinder, 160-horsepower gasoline engine, which gave her a cruising speed of 7 knots. For submerged cruising she had a sixty-cell battery, supplying electrical power to a 70-horsepower motor, which gave her a top speed of about 6 knots for about three hours and twice that endurance at slower speed. The propulsion system was versatile and flexible. The gasoline engine could be used for surface propulsion, for turning a generator to charge batteries, or for operating the air compressor. The electric motor could be used for either surface or submerged propulsion or for starting the balky gasoline engine. The battery also supplied power for the many smaller motors throughout the boat (periscope hoist, bilge pump, trim, tank pumps, etc.) and for internal lighting.

Holland founded the Electric Boat Company in New London, Connecticut, and sold submarines to any and all comers. The U.S. Navy was his first customer. In 1900 it bought the prototype Holland Holland and christened it U.S.S. and christened it U.S.S. Holland Holland (Submarine Number 1). After rigid trials, the navy bought six more Hollands for "coastal defense purposes" and later, a dozen more improved models. Alarmed by France's large-and swelling-submarine force, Great Britain's Royal Navy bought five (Submarine Number 1). After rigid trials, the navy bought six more Hollands for "coastal defense purposes" and later, a dozen more improved models. Alarmed by France's large-and swelling-submarine force, Great Britain's Royal Navy bought five Hollands Hollands in 1901 for evaluation purposes. Astonished by the efficient performance of these little craft, the British embarked on a substantial submarine buildup in 1905. That same year Holland sold submarines to the belligerents Russia and Japan, producing the seeds for the submarine forces of both those nations. in 1901 for evaluation purposes. Astonished by the efficient performance of these little craft, the British embarked on a substantial submarine buildup in 1905. That same year Holland sold submarines to the belligerents Russia and Japan, producing the seeds for the submarine forces of both those nations.

The gas-electric boat was superior to all others, but it was dangerous. Notwithstanding all efforts to prevent it, gasoline seeped into bilges, emitting explosive fumes. Deadly carbon monoxide leaked from the exhaust pipes. Several gas-electric boats in the United States and British navies blew up; some crewmen were killed bv exhaust fumes. These continuing dangers led submarine designers to explore two less volatile and toxic internal combustion fuels: paraffin (akin to kerosene) and "heavy" or "diesel" oil, named for the German inventor Rudolph Diesel, who in 1895 had demonstrated the first "heavy oil" or, as it came to be known, diesel engine.

Engineers in Germany slowly brought the paraffin and diesel engines forward. Owing to the difficulty of producing a reliable diesel engine that was compact and light enough to fit inside a submarine hull, the paraffin engine led by several years. The German arms conglomerate, Krupp A.G., was first to build a paraffin submarine-a tiny prototype, christened Forelle (Trout) Forelle (Trout), which was launched in 1902. German industry was then in good position to exploit submarine technology but it made little headway. The reason was the unyielding opposition of Grand Admiral Alfred von Tirpitz, State Secretary of the Navy. He had persuaded Kaiser Wilhelm II to embark on a massive big-ship building program, designed to outgun the big but aging Royal Navy. Singlemindedly pursuing this ambitious undertaking, von Tirpitz refused funds for unrelated, experimental, unproven weapons and discouraged all discussions of "cheap" alternatives to his big-ship navy, such as submarines.

Sensing a new and profitable market, the Krupp firm pursued the submarine in spite of von Tirpitz's indifference. In 1904 Krupp sold the Russians the paraffin Forelle Forelle and then obtained orders for three larger paraffin boats, known as the and then obtained orders for three larger paraffin boats, known as the Karp Karp class. In subsequent years it negotiated sales agreements with numerous nations (Italy, Austria-Hungary, Norway) for larger, more sophisticated paraffin boats. At the same time Krupp mounted intense pressure on German engineers to bring the diesel engine to a practical stage for submarines. class. In subsequent years it negotiated sales agreements with numerous nations (Italy, Austria-Hungary, Norway) for larger, more sophisticated paraffin boats. At the same time Krupp mounted intense pressure on German engineers to bring the diesel engine to a practical stage for submarines.

Although the staff of the German Imperial Navy concurred with von Tirpitz's big-ship program, it fretted about the submarine arms race, which was being fueled in part by German industry. It seemed imprudent to export this important military technology, which, in the wrong hands, could cause the big-ship Imperial Navy immense grief. At the least, the staff argued, the Imperial Navy should acquire a submarine for evaluation. Yielding to these pressures, von Tirpitz finally authorized Krupp to build one submarine, or Unterseeboot Unterseeboot (abbreviated as (abbreviated as U-boot U-boot, or in English, U-boat). What emerged was a slightly larger and improved copy of the paraffin-powered Karp Karp class, designated class, designated U-1 U-1. Upon her commissioning in December 1906, it was noted that Germany was not the first but rather the last major naval power to adopt submarines, and these were indebted to American technology.

Having introduced the paraffin engine and other innovations, including superb periscope optics, Krupp submarine engineers were determined to further outdo submarines of competing naval powers. Over the next several years they proposed ever larger, longer-ranged, faster, better-armed models. Still not fully persuaded that the submarine had a place in the Imperial Navy, von Tirpitz only grudgingly released funds for new construction, and in their efforts to move ahead quickly, the engineers encountered many technical setbacks. As a result, the embryonic German submarine force grew, haltingly.

The German designers, meanwhile, had been pressing ahead with grander ideas. The ambitious goal was to produce, in a single, catch-up leap, a reliable oceangoing paraffin boat about 185 feet long and with a displacement of about 500 tons. It was to be armed with four torpedo tubes (two forward, two aft), with storage space for one reload in each torpedo compartment. The designers succeeded, producing several such submarines. In the years 1908 to 1910 the Imperial Navy ordered fourteen big paraffin boats, the nucleus of the emerging German submarine force. The paraffin engine was safer than gasoline and more efficient than steam, but it had one enormous military drawback: It emitted dense white exhaust, which was visible for miles at sea. For that reason submarine designers anxiously awaited a reliable diesel engine. But it came on very slowly. The French-not the Germans-were first to fit a diesel engine in a submarine. Then the Russians. The British were next. Other nations, including Italy and the United States, turned to this new technology, but German designers, demanding higher performance and reliability, held off. However, in 1910 Germany finally curtailed construction of paraffin boats and shifted to diesel, the last major power to do so. In the period 1910-1912 the Imperial Navy ordered twenty-three diesel-electric boats.

By the summer of 1914, on the eve of World War I, the submarine arms race, scarcely a dozen years old, had produced an astounding number of boats worldwide: about 400. Many of these were "old technology" gasoline- or steam-propelled submarines of limited or no military value, but a fourth of the boats were modern oceangoing diesel-electrics, armed with four or five torpedo tubes. Great Britain-not Germany-had the largest submarine fleet: seventy-six, with another twenty on the building ways. France ranked second, with seventy boats (many steam-electric) and twenty-three under construction. Czarist Russia came third with forty-one boats, most of them obsolescent. The United States ranked fourth with thirty-one, and eight more under construction. Germany held fifth place with twenty-six commissioned boats and fifteen under construction.

Undefined as yet was the role submarines were to play in war. Originally conceived as small, short-legged "coast" and "harbor" defensive weapons to thwart or counter enemy raids and blockades, they had grown into offensive oceangoing craft with substantial durability and firepower. They were believed to be capable of waging war against enemy battle fleets, acting alone or as part of a group. They were also capable of hit-and-run attacks on an enemy's maritime commerce in a guerre de course guerre de course. Mounted systematically and with great intensity, a submarine guerre de course guerre de course could produce a new kind of blockade, to which the "island" nation of Great Britain would be peculiarly vulnerable. could produce a new kind of blockade, to which the "island" nation of Great Britain would be peculiarly vulnerable.

However, a submarine guerre de course guerre de course, or war on commerce, would impose numerous legal, moral, and practical difficulties. Over the centuries civilized nations had evolved rules and regulations known as "prize laws" with respect to commerce raiding and had pledged in various international treaties to abide strictly by them. No merchant vessel of any kind was to be sunk at first sight without warning. Specific procedures were to be followed. The interceptor was required first to stop the merchant ship by signal or, if necessary, "a shot across the bow." The interceptor was then required to establish by a ritualized procedure (known as "visit and search") whether the accosted ship was friend, foe, or neutral. If found to be a friend or a neutral transporting innocent or innocuous cargo, the ship was allowed to proceed unmolested. If found to be a foe, or a foe disguised as a neutral, or a neutral transporting "contraband" (i.e., war materiel or other prohibited cargo) to the enemy, the interceptor was permitted to capture (or sink) a foe and to capture an offending neutral. A captured ship was to be manned by a "prize crew" and sailed to a friendly or neutral port and turned over to a legal tribunal. Judges would then decide whether or not the capture had been legally correct and if the neutral's cargo was indeed contraband. If the tribunal condemned the neutral for transporting contraband, both ship and cargo could be sold at auction and the proceeds distributed to the interceptor or its sponsoring government. If, on the contrary, the tribunal found the interceptor to have incorrectly interpreted the cargo as contraband, the interceptor and/or its sponsoring government was subject to fines and damages.*

Beyond that there had evolved a strict, humane code of the sea with respect to the crews of merchant vessels. In various international treaties it had been agreed that merchant ship crews-and passengers-were "noncombatants" and were not to be harmed or abandoned. If the interceptor found it necessary to sink the merchant vessel for whatever reason, it was required to take aboard the crewmen and passengers and land them ashore or to place them (and the ship's papers) in sound lifeboats, well supplied with provisions, sails, and navigational equipment, and give them specific directions and courses to the nearest land, or, if known, the nearest neutral ship thereabouts. Any violation of this code would be considered inhumane and barbarous and subject to severe punishment. it had been agreed that merchant ship crews-and passengers-were "noncombatants" and were not to be harmed or abandoned. If the interceptor found it necessary to sink the merchant vessel for whatever reason, it was required to take aboard the crewmen and passengers and land them ashore or to place them (and the ship's papers) in sound lifeboats, well supplied with provisions, sails, and navigational equipment, and give them specific directions and courses to the nearest land, or, if known, the nearest neutral ship thereabouts. Any violation of this code would be considered inhumane and barbarous and subject to severe punishment.

Submarines waging a guerre de course guerre de course could not conveniently or safely abide by all these complicated rules. To do so would surrender the submarine's greatest asset: surprise in the attack. Stopping a ship by signal or a shot across the bow on the high seas for the ritualized "visit and search" would be an extremely difficult undertaking. The submarine would have to come to the surface, where it was most vulnerable. Many merchant ships could simply bend on more steam and outrun even the most modern submarines, which could make only 12 to 15 knots. A bold merchant ship captain might even attempt to ram the submarine. could not conveniently or safely abide by all these complicated rules. To do so would surrender the submarine's greatest asset: surprise in the attack. Stopping a ship by signal or a shot across the bow on the high seas for the ritualized "visit and search" would be an extremely difficult undertaking. The submarine would have to come to the surface, where it was most vulnerable. Many merchant ships could simply bend on more steam and outrun even the most modern submarines, which could make only 12 to 15 knots. A bold merchant ship captain might even attempt to ram the submarine.

Assuming the ship did stop on signal, the "visit and search" ritual presented other difficulties. Submarines did not carry enough manpower or small boats to board a merchant ship for a proper inspection. A small boarding party that went over on a rubber raft could be captured and held hostage, leaving the submarine captain to face the unwelcome choice of letting the ship (and his captured men) proceed or torpedoing it with the probable loss of his men. Should these difficulties be surmounted and the ship found to be a neutral with a contraband cargo, with the limited manpower available, it would be exceedingly difficult to capture the ship, man it with a "prize crew," and sail it to a friendly or neutral port for legal adjudication. If the ship was to be sunk for whatever reason, the submarine could not take the crew aboard and land it ashore or otherwise provide much meaningful assistance. It would be necessary for the submarine to wait for the crew to provision its lifeboats, abandon ship, and stand well clear of torpedoes or gunfire, a tedious, high-risk process that would expose the submarine to constant danger of sudden counterattack from enemy naval forces.

These considerations were much discussed behind closed doors in naval establishments and in professional journals. Some navalists, including Britain's foremost submarine advocate John (Jacky) Fisher, concluded that if submarines engaged in a guerre de course guerre de course, the prize laws could in no way be adhered to. "However inhuman and barbarous it may appear," Fisher wrote in a prescient, prewar paper, "there is nothing else the submarine can do except sink her captives." In response, Winston S. Churchill, First Lord of the Admiralty* in 1911, spoke for many British naval officers: "I do not believe this would ever be done by a civilized Power." Hence on the eve of World War I, the gentlemanly and naive assumption that submarines would only attack enemy warships was the prevailing view. in 1911, spoke for many British naval officers: "I do not believe this would ever be done by a civilized Power." Hence on the eve of World War I, the gentlemanly and naive assumption that submarines would only attack enemy warships was the prevailing view.

U-BOATS IN W WORLD W WAR I.

When World War I commenced in early August 1914, the German Imperial Navy had not completed its big-ship buildup. The High Seas Fleet was therefore not strong enough to sail out and confront Britain's powerful Grand Fleet in a single, decisive battle. Nor was the Royal Navy capable of mounting a decisive attack on the Imperial Navy in its home waters. Hence a big-ship standoff ensued, during which the opposing admirals schemed ways to entrap the other's fleet in the confined waters of the North Sea by guile and deception. The naval war between these two great maritime powers thus proceeded in a curious, cautious, and unforeseen manner. There was only a single major surface-ship battle-Jutland-and it was brief and inconclusive.

Early in the war both Germany and Great Britain deployed submarines on offensive missions. The initial forays were remarkable. German U-boats sank three British heavy cruisers (Aboukir, Hague, and Cressy Cressy) and two light cruisers (Pathfinder, Hawke) with the loss of over 2,000 men. British submarines sank the German light cruiser Hela Hela. Both navies were thus compelled to view the submarine as a grave new threat and they reacted accordingly. The British Grand Fleet withdrew temporarily from its North Sea base in Scapa Flow to safer waters in north Ireland. The German High Seas Fleet sharply curtailed operations in its home waters, the Helgoland Bight.

The British imposed a naval blockade against Germany with the aim of shutting off the flow of war materiel. The British did not strictly observe the prize laws; even neutral ships loaded merely with food were harassed, blocked, or turned back. In retaliation, the German Naval Staff authorized German U-boats to harass Allied merchant shipping. On October 20, 1914, a U-boat, observing the prize laws, stopped, searched, and scuttled the 866-ton British freighter Glitra Glitra off Norway. A week later another U-boat, operating in the English Channel, torpedoed without warning a French steamer, off Norway. A week later another U-boat, operating in the English Channel, torpedoed without warning a French steamer, Admiral Ganteaume Admiral Ganteaume, which was believed to be laden with troops and therefore fair game under the prize laws. In fact the ship was jammed with 2,400 Belgian refugees, including many women and children. Fortunately, it did not sink.

These two U-boat attacks on unarmed merchant ships carried profound implications for the island nation of Great Britain, entirely dependent upon her vast mercantile fleet for survival. An organized U-boat guerre de course guerre de course might be ruinous. Accordingly, the British government denounced the attacks as illegal, treacherous, piratical, and immoral. Ship owners, merchants, and insurance carriers the world over joined the chorus of denunciation. might be ruinous. Accordingly, the British government denounced the attacks as illegal, treacherous, piratical, and immoral. Ship owners, merchants, and insurance carriers the world over joined the chorus of denunciation.

The Central Powers, composed of Germany and the Austro-Hungarian Empire, had planned to defeat France in a quick campaign, then turn about and crush czarist Russia. But the plan went awry. The armies in France bogged down in bloody trench warfare; Russia attacked from the east, creating a two-front war. Not having anticipated a long war, the Central Powers had not stockpiled large supplies of war materiel. As a result of the British blockade, by early 1915 the Central Powers were running out of iron ore and oil and other war essentials as well as food.

To this point U-boats, strictly observing the prize rules, had sunk ten British merchant ships for about 20,000 tons. Owing to the shortage of torpedoes-they were still virtually handmade-most of these sinkings had been achieved by gunfire or forced scuttling. The surprising ease of these successes had led the senior German admirals to conclude that if the prize rules were relaxed, even the small number of U-boats available for distant operations could impose an effective counterblockade on the British Isles. The mere appearance of a single U-boat, manned by only two dozen men, whether successful in the attack or not, caused great psychological alarm, compelling the enemy to devote a hugely disproportionate share of his manpower and resources to neutralize the threat. All this would severely impair Britain's ability to carry on the war, the advocates postulated, and might result in a tit-for-tat deal in which Britain agreed to lift its blockade of Germany.

Neither the Kaiser nor his Chancellor was keen on the proposal. Germany had already incurred heavy criticism from many quarters for sinking merely ten merchant ships. A relaxation of the prize rules would doubtless draw even harsher criticism, especially from neutral nations such as the United States, which had a substantial financial interest in sea commerce and might retaliate by entering the war. Moreover, the number of U-boats available for blockading the British Isles seemed too slight. To announce a blockade and fail abjectly would be worse than no attempt at all.

And yet the proposal would not die. Its advocates argued, not without justification, that the moral arguments were no longer relevant. In its ruthless blockade of Germany, they insisted, Britain had repeatedly violated the prize rules and other traditions protecting sea commerce, most notably in refusing the passage of neutral ships carrying only food. This line of reasoning, and other arguments, finally persuaded the Kaiser and his Chancellor to authorize a U-boat blockade of Great Britain.

The stage was carefully set. The Kaiser publicly declared that from February 18, 1915, onward, the waters around the British Isles were to be considered a "war zone." Prize rules would no longer be strictly observed. British and French merchant vessels would be sunk without warning or exceptional measures to provide for the safety of the crews. Care would be taken to spare neutrals not carrying contraband, but all neutrals would sail the waters at their own peril. U-boat skippers, the Kaiser further declared, would not be held responsible if "mistakes should be made."

So was launched history's first systematized submarine guerre de course guerre de course. The initial results were less than impressive. In the month of February 1915, the twenty-nine U-boats of the German submarine force sank 60,000 tons of merchant shipping; in March, 80,000 tons. The weakness of the blockade lay in the small number of U-boats available. Owing to the time spent going to and from German bases and in refit, after the initial deployment it was difficult to establish organized U-boat patrol cycles that kept more than six or seven U-boats in British waters at any given time. Notwithstanding the fear and confusion and diversion of resources it precipitated, the first U-boat blockade did not achieve its main goal. First Lord Churchill declared the blockade a failure; British imports in 1915 exceeded those of 1913. The British government refused to entertain any suggestion of lifting the blockade of Germany.

With each merchant ship sinking, the cries of moral indignation intensified. Three sinkings in particular outraged the Americans: the 32,500-ton Cunard liner Lusitania Lusitania on May 7, with the loss of 1,198 passengers (128 Americans) and crew; the 16,000-ton White Star liner on May 7, with the loss of 1,198 passengers (128 Americans) and crew; the 16,000-ton White Star liner Arabic Arabic on August 19, with the loss of 40 passengers (3 Americans); and the liner on August 19, with the loss of 40 passengers (3 Americans); and the liner Hesperian Hesperian on September 9. So violent was the reaction in the United States (U-boat crews make war "like savages drunk with blood" declared on September 9. So violent was the reaction in the United States (U-boat crews make war "like savages drunk with blood" declared The New York Times The New York Times), that in early September 1915 the Kaiser called off the blockade of Great Britain and sent many more U-boats to the Mediterranean Sea, where the hunting was less controversial and no less lucrative and there were few Americans.

With victory no closer for the Central Powers, at the beginning of 1916 the chief of the German naval staff, Admiral Henning von Holzendorff, and his Army counterpart urged the Kaiser to authorize a renewal of the British blockade. The Navy now had almost twice as many U-boats in commission (fifty-four versus twenty-nine in 1915) and ever more U-boats were coming off the slipways. The Kaiser was tempted, but the Chancellor and Foreign Minister objected, fearful of another Lusitania Lusitania, which would almost certainly bring America into the war. After days of vacillation, the Kaiser sided with the Navy, but he imposed complicated restrictions. No passenger liners of any nationality were to be attacked anywhere. No cargo ships or tankers except those unmistakably armed could be attacked outside the war zone.

The renewed blockade commenced in February 1916. Notwithstanding the restrictions and complexity of the rules, all went well for the U-boats for two months: 117,000 tons sunk in February, 167,000 tons in March. Then came another costly error. On March 24 a U-boat mistook the 1,350-ton English Channel passenger ferry Sussex Sussex for a troopship and torpedoed it. The for a troopship and torpedoed it. The Sussex Sussex did not sink, but about eighty people were killed in the explosion, including twenty-five Americans. In response to the renewed cries of indignation and a blistering note from Washington threatening to sever diplomatic relations, the Kaiser backed down once more and, on April 24, ordered U-boats in waters of the British Isles again to adhere strictly to the prize rules. As a result, merchant ship tonnage sunk by U-boats in British waters fell sharply for the next four months. did not sink, but about eighty people were killed in the explosion, including twenty-five Americans. In response to the renewed cries of indignation and a blistering note from Washington threatening to sever diplomatic relations, the Kaiser backed down once more and, on April 24, ordered U-boats in waters of the British Isles again to adhere strictly to the prize rules. As a result, merchant ship tonnage sunk by U-boats in British waters fell sharply for the next four months.

The German submarine force had grown to substantial size by September 1916: a total of 120 boats of all types, many with larger 105mm (4.1") deck guns. Again the military staffs urged the Kaiser to exploit this force to the fullest. Again the Kaiser vacillated, and finally yielded, but with yet a new set of rules. Skippers were to conduct only restricted submarine warfare (by prize rules) in waters of the British Isles, where there were numerous American and other neutral ships, but they were permitted to wage unrestricted submarine warfare in the Mediterranean. This third and most intense phase of the restricted U-boat war, October 6, 1916, to February 1, 1917, was highly productive for the Germans. The U-boats sank about 500 British merchant vessels for about 1.1 million tons, raising the total bag for 1916 to about 2.3 million tons, most of that of British registry.

By early 1917 the ground war had become a brutal and fruitless bloodletting for the Central Powers and there was deep and widespread unrest at home. The German military staffs urged the Kaiser to authorize unrestricted submarine warfare in all oceans and seas. Using the results achieved in the fall of 1916, the larger number of U-boats available, plus nearly ninety new boats that were to be commissioned in 1917, the naval staff calculated that with an unrestricted U-boat campaign, nearly half of Britain's still large merchant fleet could be wiped out within five or six months, rendering her not only incapable of prosecuting the war on the continent but also leaving her population in a condition of starvation and rebellion. America be damned, the naval staff said. If she came into the war, Germany would have enough U-boats (about seventy ready for operations in the British Isles alone) to sink all her troop and supply ships before they reached Europe. By that time, too, there was no shortage of German submarine torpedoes; U-boat skippers did not have to rely so heavily on deck guns.

Turning aside peace feelers from President Wilson and others, the Kaiser approved this proposal. He announced to the world that commencing February 1, 1917, U-boats would sink on sight every merchant ship found in British territorial waters. At the same time, he assured the German military staffs that there would be no more pussyfooting or backing down, and he promulgated a radical role reversal for the surface ships of the Imperial Navy: Henceforth they were to support U-boats, rather than the other way around. "To us," he said, "every U-boat is of such importance that it is worth using the whole available fleet to afford it assistance and support."

Germany launched this all-out submarine guerre de course guerre de course in the British Isles with multiple attacks conducted simultaneously with "utmost energy" by about sixty U-boats. To minimize detection by Allied aircraft and submarines, and counterfire from merchant ships, and to take advantage of higher speed for escape, U-boat skippers attacked at night while on the surface. The results were spectacular: 540,000 tons sunk in February, 594,000 tons in March, and an appalling 881,000 tons in April. During April alone-the grimmest month of the U-boat war-the Germans sank 423 merchant ships, of which 350 were British. in the British Isles with multiple attacks conducted simultaneously with "utmost energy" by about sixty U-boats. To minimize detection by Allied aircraft and submarines, and counterfire from merchant ships, and to take advantage of higher speed for escape, U-boat skippers attacked at night while on the surface. The results were spectacular: 540,000 tons sunk in February, 594,000 tons in March, and an appalling 881,000 tons in April. During April alone-the grimmest month of the U-boat war-the Germans sank 423 merchant ships, of which 350 were British.* Moreover, as anticipated, the campaign scared off most of the many neutral ships trading with Great Britain. Moreover, as anticipated, the campaign scared off most of the many neutral ships trading with Great Britain.

Reflecting the growing anger and outrage in America, President Wilson reacted firmly and militantly to this all-out U-boat campaign. On the third day, February 3, 1917, he broke off diplomatic relations with Germany. At his request, on April 6 the Congress declared war on the Central Powers.

At the beginning of the war the Royal Navy possessed no special countermeasures to fight submarines. Naval tacticians wrongly assumed that since submarines would of necessity spend most of the time on the surface, they would be easy prey for gunfire and ramming. This wrong view was reinforced when the British cruiser Birmingham Birmingham rammed and sank rammed and sank U-15 U-15, the first U-boat to be lost. But in the five months of warfare in 1914, the Royal Navy positively sank only one other U-boat, U-18 U-18. Three other U-boats were lost in 1914 (for a total of five) to unknown causes, probably mines.

Beginning in 1915, when shipping losses to U-boats began to climb significantly, the Admiralty diverted a substantial portion of its existing resources to antisubmarine warfare (A/S in Britain, ASW in America) and asked scientists, engineers, academics, and others to help develop ways to destroy U-boats. In the belief that the best defense was a strong offense, the chief ASW weapons to emerge in World War I were these: * S SURFACE H HUNTERS. The Admiralty sent scores, then hundreds, then thousands of surface ships out offensively scouring the oceans for U-boats. These vessels included destroyers, frigates, sloops, trawlers, yachts, and heavily armed raiders (Q-ships) disguised as tramp steamers. Some vessels were fitted with crude hydrophones-passive underwater listening devices-which could detect the engine noise of a surfaced U-boat, but only if the hunting vessels were not moving.

In 1916 many of these offensive ASW ships were armed with a new weapon called the depth charge. The best of these underwater bombs, derived from mines, contained 300 pounds of TNT or Amatol and were fitted with hydrostatic fuses which could be set to detonate the charges at 40 and 80 feet, and later 50 to 200 feet. Since early depth charges were rolled from stern tracks (or racks) and exploded at shallow depth, the attacking vessel had to put on maximum speed or risk severe damage to its stern. Therefore, slower vessels could not use the 300-pound depth charges until fuses with deeper settings had been developed. In all of 1916, British naval forces sank only two U-boats by depth charge. In 1917 and 1918, when depth charges had been improved and were much more plentiful, the kill rate by this weapon increased significantly.

* A AIRBORNE H HUNTERS. When the war commenced, the aviation age was merely a dozen years old. The Royal Navy had acquired about fifty seaplanes and seven nonrigid airships, called "blimps," to scout for enemy naval forces. Some of these aircraft were diverted to U-boat hunting but, owing to the unreliability of engines, slow speed, limited fuel capacity, tiny bomb loads, and other factors, they were useless against U-boats. It became apparent, however, that when an aircraft appeared near a U-boat, it dived and became essentially immobile. Hence air patrols were useful for forcing U-boats under, thus enabling ships to skirt the danger area and avoid attack. In 1915 the Royal Navy acquired much improved seaplanes (the American-designed Curtiss American) and blimps in greater numbers. These were armed with impact-fused 100- or 520-pound bombs or 230-pound ASW bombs with delayed-action fuses that exploded at a water depth of seventy feet, but the U-boat kill rate by aircraft remained essentially zero. When the war commenced, the aviation age was merely a dozen years old. The Royal Navy had acquired about fifty seaplanes and seven nonrigid airships, called "blimps," to scout for enemy naval forces. Some of these aircraft were diverted to U-boat hunting but, owing to the unreliability of engines, slow speed, limited fuel capacity, tiny bomb loads, and other factors, they were useless against U-boats. It became apparent, however, that when an aircraft appeared near a U-boat, it dived and became essentially immobile. Hence air patrols were useful for forcing U-boats under, thus enabling ships to skirt the danger area and avoid attack. In 1915 the Royal Navy acquired much improved seaplanes (the American-designed Curtiss American) and blimps in greater numbers. These were armed with impact-fused 100- or 520-pound bombs or 230-pound ASW bombs with delayed-action fuses that exploded at a water depth of seventy feet, but the U-boat kill rate by aircraft remained essentially zero.

* S SUBMERGED H HUNTERS. On the theory that it was wise to "send a thief to catch a thief," the Royal Navy saturated German home waters with submarines equipped with hydrophones. The early patrols produced no confirmed kills, but the presence of British submarines in German waters, including the Baltic Sea, where German submariners trained, caused great anxiety and disrupted routines. Beginning in 1915, British submarines began to torpedo U-boats in significant numbers. The Admiralty designed and produced a small submarine ( On the theory that it was wise to "send a thief to catch a thief," the Royal Navy saturated German home waters with submarines equipped with hydrophones. The early patrols produced no confirmed kills, but the presence of British submarines in German waters, including the Baltic Sea, where German submariners trained, caused great anxiety and disrupted routines. Beginning in 1915, British submarines began to torpedo U-boats in significant numbers. The Admiralty designed and produced a small submarine (R class) specifically for U-boat hunting but it came too late. Had British torpedoes been more reliable, the submarines doubtless would have sunk many more U-boats. class) specifically for U-boat hunting but it came too late. Had British torpedoes been more reliable, the submarines doubtless would have sunk many more U-boats.

* M MINES. From the first days of the war both sides employed moored contact mines, planted in shallow water, usually defensively but often offensively. Defensive minefields were sown to prevent enemy forces from penetrating one's coastal waters for shore bombardment, interdiction of shipping, or invasion. Such minefields were charted and planted with great care, leaving secret safe lanes for friendly shipping and naval forces. In order to attack British shipping, U-boats often had to negotiate the periphery or heart of defensive minefields, a hazardous undertaking. Many U-boats strayed into British minefields or hit live mines that had drifted their moorings or had broken loose. Offensive mining was more complicated and often hit-or-miss. Surface vessels, operating under cover of darkness in great haste, planted mines in likely spots such as sea-lanes or sometimes even in the safe lanes of the defensive minefields, to catch opposing naval vessels or merchant ships by surprise. Later in the war, both sides employed submarines for minelaying, combining two much-feared naval weapons. From the first days of the war both sides employed moored contact mines, planted in shallow water, usually defensively but often offensively. Defensive minefields were sown to prevent enemy forces from penetrating one's coastal waters for shore bombardment, interdiction of shipping, or invasion. Such minefields were charted and planted with great care, leaving secret safe lanes for friendly shipping and naval forces. In order to attack British shipping, U-boats often had to negotiate the periphery or heart of defensive minefields, a hazardous undertaking. Many U-boats strayed into British minefields or hit live mines that had drifted their moorings or had broken loose. Offensive mining was more complicated and often hit-or-miss. Surface vessels, operating under cover of darkness in great haste, planted mines in likely spots such as sea-lanes or sometimes even in the safe lanes of the defensive minefields, to catch opposing naval vessels or merchant ships by surprise. Later in the war, both sides employed submarines for minelaying, combining two much-feared naval weapons.

To prevent U-boats from reaching the Atlantic via the English Channel, the British sowed lines of mines across it from Dover, England, to Cape Gris-Nez, France. However, in 1915 and 1916, British contact mines were defective, and not until the Admiralty copied and mass-produced the standard German contact mine could the Dover "field" be depended upon to block the passage of U-boats. When the Dover field was finally effective, it forced U-boats destined for the Atlantic to go northabout Scotland, adding about 1,400 miles (and about seven days) to the voyage.

After the United States entered the war and offered the Royal Navy a secret mine with a magnetic fuse, the Allies put in motion a grandiose scheme to plant 200,000 such mines across the top of the North Sea from the Orkney Islands to Norway. Although American and British forces planted about 80,000 mines in this so-called Northern Barrage, most of these mines were also defective and, other than frayed nerves, caused the Germans small harm. Even so, Allied mines in all areas ranked high as U-boat killers.

* R RADIO I INTELLIGENCE. When the war began, radio transmission or wireless telegraphy (W/T) was a new military technology at which the British excelled. Taking advantage of a lucky capture of German naval codebooks, as well as an appalling lack of sophistication in German radio procedures and security, the British thoroughly penetrated German naval communications. The British first perfected Radio Direction Finding (RDF) to pinpoint and identify German shore- and sea-based transmitters. Utilizing the captured codebooks, they "read" on a current basis most German naval transmissions. This priceless intelligence enabled the Admiralty's secret signals-intelligence branch (known as Room 40) to track U-boat operations to a remarkable extent. A British historian wrote that by "early 1915, Room 40 knew the total strength of the U-boat fleet, the rate at which it was growing ... the composition of each flotilla ... the number of U-boats at sea or in port, and when and if it put to sea ... losses, as evidenced by the failure of a U-boat to return, and in most cases, the size of the [U-boat] threat in any particular area." When the war began, radio transmission or wireless telegraphy (W/T) was a new military technology at which the British excelled. Taking advantage of a lucky capture of German naval codebooks, as well as an appalling lack of sophistication in German radio procedures and security, the British thoroughly penetrated German naval communications. The British first perfected Radio Direction Finding (RDF) to pinpoint and identify German shore- and sea-based transmitters. Utilizing the captured codebooks, they "read" on a current basis most German naval transmissions. This priceless intelligence enabled the Admiralty's secret signals-intelligence branch (known as Room 40) to track U-boat operations to a remarkable extent. A British historian wrote that by "early 1915, Room 40 knew the total strength of the U-boat fleet, the rate at which it was growing ... the composition of each flotilla ... the number of U-boats at sea or in port, and when and if it put to sea ... losses, as evidenced by the failure of a U-boat to return, and in most cases, the size of the [U-boat] threat in any particular area."

Still, these many and varied ASW measures were absurdly inadequate. In all of 1915 the Germans lost merely nineteen U-boats while adding fifty-two boats to the force. In 1916 the Germans lost twenty-two boats while adding 108 boats. Notwithstanding a massive British antisubmarine effort, during the first four months of 1917, the Germans lost only eleven U-boats. To then, the average monthly U-boat loss rate had been only 1.7, a continuing losing battle for Britain because the Germans were producing seven or eight new boats per month.

In the wake of the spectacular shipping losses in April 1917, Britain's new Prime Minister, David Lloyd George, urged the Admiralty to organize British shipping into convoys, escorted by destroyers, frigates, sloops, and other ASW craft. This was hardly a new idea; defense of sea commerce by convoy was as old as the sail and, as the British naval historian John Winton put it, "as natural and as obvious a tactic as, say, gaining and keeping the weather gauge."

The Royal Navy had opposed the formation of convoys for numerous reasons. The principal reason, Winton wrote, was that Royal Navy officers had forgotten their history-that the main purpose of the Royal Navy was to protect Britain's sea trade. Imbued with the aggressive doctrines of the American naval theorist Alfred Thayer Mahan (and kindred souls), who postulated that control of the seas could most effectively be insured by husbanding naval assets for a single, decisive, offensive naval battle with the enemy, they opposed the diversion of naval resources to convoying, which they viewed as mundane and defensive and which, if adopted, would be an admission that Britain had, in effect, lost control of the seas to an inferior naval power.

There were other reasons. First, notwithstanding huge losses of merchant ships on their very doorstep, the Royal Navy continued to grossly underestimate the overall effectiveness of the U-boat campaign on British maritime assets. Second, the admirals insisted convoys were enormously inefficient, compelling faster ships to reduce speeds to those of slower ships, overwhelming seaport facilities during loading and unloading periods, and posing difficult organizational problems in distant, neutral ports. Third, the Admiralty doubted the ability or desire of merchant-ship captains to accept or to follow orders or to station-keep in the required tight zigzagging formations at night or in inclement weather. Fourth, the admirals held, the concentration of merchant ships into a single large body presented U-boat skippers with richer targets, which they were not likely to miss, even with poorly aimed or errant torpedoes.

With the assistance of American naval power, the Admiralty finally-and reluctantly-agreed to a test of inbound convoying in the Atlantic. The first convoy, consisting of sixteen ships, sailed from Gibraltar to the British Isles on May 10, 1917; the second of twelve ships from Norfolk, Virginia,* on May 24. The Gibraltar convoy arrived in good time without the loss of a ship. The Norfolk convoy, escorted by the British cruiser on May 24. The Gibraltar convoy arrived in good time without the loss of a ship. The Norfolk convoy, escorted by the British cruiser Roxburgh Roxburgh and six American destroyers, ran into minor difficulties. Two of the dozen ships could not maintain the convoy's 9-knot average speed and fell out. One of these was torpedoed going into Halifax, Nova Scotia. However, the other ten ships crossed the Atlantic in foggy weather, maintaining tight formation, zigzagging all the way, and arrived safely in the British Isles. and six American destroyers, ran into minor difficulties. Two of the dozen ships could not maintain the convoy's 9-knot average speed and fell out. One of these was torpedoed going into Halifax, Nova Scotia. However, the other ten ships crossed the Atlantic in foggy weather, maintaining tight formation, zigzagging all the way, and arrived safely in the British Isles.

With the results of these tests and other data in hand, in August 1917-the beginning of the fourth year of the war-the Admiralty finally adopted the convoy system. It was a smashing success. By October over 1,500 merchant ships in about 100 convoys had reached the British Isles. Only ten ships were lost to U-boats while sailing in these convoys: one ship out of 150. By comparison, the loss rate for ships sailing independently (inbound and otherwise) was one in ten. By the end of 1917, almost all of the blue-water traffic was convoyed. These convoys had been instituted in the nick of time; U-boats sank nearly 3,000 ships for 6.2 million tons in 1917, most of them sailing independently. The historian Winton wrote: "Convoying did not win the war in 1917. But it did prevent the war from being lost in 1917."

A U-boat skipper remembered the impact of convoying on the German submarine force. Convoying, he wrote, "robbed it of its opportunity to become a decisive factor." He continued: "The oceans at once became bare and empty; for long periods at a time the U-boats, operating individually, would see nothing at all; and then suddenly up would loom a huge concourse of ships, thirty or fifty or more of them, surrounded by a strong escort of warships of all types." The solitary U-boat, he went on, which "had most probably sighted the convoy purely by chance," would attempt to attack again and again, "if the commander had strong nerves" and stamina. "The lone U-boat might sink one or two of the ships," he concluded, "or even several; but that was a poor percentage of the whole. The convoy would steam on."

During the final twelve months of the war, convoying became the rule rather than the exception. The British and American navies established large organizations to administer convoys and provided surface and, where feasible (close to land), aircraft escorts, armed with new and improved aerial bombs. In many instances, intelligence from Room 40, accurately identifying U-boat positions, enabled the authorities to divert convoys away from U-boats. After the full convoy system was in place (outbound from the British Isles as well as inbound) in 1918, total shipping losses fell by two-thirds from 1917: 1,133 sunk. Of these, 999 sailed independently. In the ten months of naval war in 1918, only 134 ships were lost in convoy.

The United States Navy had entered the war itching for a grand, Mahan-like decisive naval battle. Like the Royal Navy, it soon discovered that was out of the question. In due course, its main efforts were directed at helping the British fight the U-boat. It provided scores of destroyers and other small vessels for ASW hunter-killer groups and convoy escort as well as minelayers for the Northern Barrage. It also sent submarines (twenty-three in all) to conduct ASW patrols in the Azores and British Isles, but neither the boats nor the crews were up to the task, and none had any success. However, the infusion of U.S. Navy surface forces during the second half of 1917 enabled the British to convoy on a large scale and contributed to a doubling of the U-boat loss rate in 1917: forty-three U-boats lost, compared with the twenty lost in the first six months.