"This will do," said Jack, leaning close to Frank. "They'll overtake us, but believing we are of their number, there is little likelihood that they will investigate us very closely. We can fall in line without trouble and accompany them wherever they go."

"Suits me," said Frank. "Just keep me posted on their proximity."

Gradually the Germans reduced the distance and at length the first plane was only a few yards behind the craft in which Frank and Jack were risking their lives. The German craft flashed by a moment later without paying any attention to the hydroplane.

"Little more speed, Frank," called Jack.

The hydroplane skimmed through the air faster than before and the next German craft did not overtake it so easily; but at length it pa.s.sed, as did a third and a fourth.

"Here's a good place for us to fall in line," Jack instructed.

Again Frank increased the speed of the hydroplane and it moved swiftly in the wake of the fourth German craft. After that no enemy air plane pa.s.sed them.

"Any idea where we are?" asked Frank of his chum.

"We're not far off the Belgian coast, but how far west I can't say,"

returned Jack. "Don't suppose it makes any particular difference, though."

"I guess not."

Frank became silent and gave his undivided attention to keeping the German plane ahead of him in sight.

And in this manner they proceeded for perhaps another half hour.

Then the machine ahead of Frank veered sharply to the south. Frank brought the head of his own craft in the same direction and the flight continued.

"Headed for the Belgian or French coast, apparently," said Jack to himself. "Wonder what the idea is?"

Now the craft ahead of that in which the two boys rode reduced its speed abruptly. Frank cut down the gait of his own craft and they continued on their way more slowly.

"Nearing our destination, wherever that is," muttered Jack.

The lad felt of his revolvers to make sure that they were ready in case of an emergency.

"Land ahead," said Frank, suddenly.

Jack gazed straight before him. There, what appeared to be many miles away, though in reality it was but a few, was a dark blur below.

Occasionally what appeared to be little stars twinkled there. Jack knew they were the lights of some town.

"Guess that's where we are headed for, all right," he told himself.

Behind the British hydroplane the other German airships came rapidly, keeping some distance apart, however. Jack leaned close to Frank.

"Just do as the ones ahead of you do," he said quietly. "I don't know where we are nor what is likely to happen. Keep your nerve and we'll be all right."

"Don't worry about me," responded Frank. "I'm having the time of my life."

Jack smiled to himself, for he knew that Frank was telling the truth.

There was nothing the lad liked better than to be engaged in a dangerous piece of work and more than once his fondness for excitement had almost ended disastrously.

"Frank's all right if he can just keep his head," muttered Jack. "I'm likely to have to hold him in check a bit, though."

They had approached the sh.o.r.e close enough now to perceive that the distant lights betokened a large town.

"Probably Ostend," Jack told himself, "though why they should come this way is too deep for me."

But Jack was wrong, as he learned a short time later.

The town that they now were approaching was the French port of Calais and it was still held by the French despite determined efforts of the Germans at one time or another to extend their lines that far. The capture of Calais by the Germans would have been a severe blow to England, for with the French seaport in their possession, the Germans, with their great guns, would have been able to command the English channel and a considerable portion of the North Sea coast.

When it appeared that the German aircraft would fly directly over the city, the leading machine suddenly swerved to the east. The others followed suit.

The night was very dark, and in spite of the occasional searchlight that was flashed into the air by the French in Calais, the Teuton machines so far had been undiscovered. Now, hanging low over the land, a sudden bombardment broke out from the German air planes.

It was not the sound of bombs that came to the lads' ears; rather the sharp "crack! crack!" of revolver firing. Jack and Frank gazed about them quickly, for they believed, for the moment, that the Germans had encountered a squadron of French airships.

But there was no other machine in sight save the German craft.

"What in the world is the meaning of this?" Frank asked of Jack.

"Don't know," returned the lad, "but I guess I'd better join in."

He drew his revolver and fired several shots in the air.

"Seems to be expected of us," he said. "We don't want to disappoint them."

The German aircraft now headed straight for the city of Calais. Frank sent his machine speeding in the same direction. Then, just as it appeared they would fly directly above the city, the first German craft began to descend. The others did likewise and a moment or so later they all came to earth in the center of what Frank and Jack could see was a small army camp; and as they alighted from their machines, the lads saw that it was an Allied camp and not a German.

"Must be Calais," said Frank to Jack in a whisper. "Have we been mistaken? Are these French and British machines?"

"Well, it looks like it," returned Jack. "We'll keep quiet and let the other fellows do the talking."

A French officer now approached the pilot of the first aircraft.

"We heard the firing aloft a moment ago," he said. "Did you encounter the enemy?"

"We were pursued all the way from the German lines," was the reply.

"Anyone hit?"

"I think not, though I believe we accounted for one or two of the enemy."

"Good. Will you fly again tonight?"

"Yes; but not before midnight."

The French officer withdrew.