The flash of a revolver from the disabled craft interrupted him. It was closely followed by another and then two more.

With a sudden move, Frank changed the course of the hydroplane. He felt a sharp pain in his left shoulder.

"Got me," he called to Jack.

The latter was alarmed.

"Where?" he demanded.

"Left shoulder," said Frank, quietly. "Nothing serious, though."

Jack levelled his revolver and fired rapidly at the enemy. His pains were rewarded by howls of derision.

"They tricked us, all right," said Jack, as he reloaded.

"That's what they did. I should have known better, too. They almost settled us."

"We've got to get them, some way," declared Jack.

"Show me how, and I'll go along with you," declared Frank.

"Well, I've got a scheme, but I don't know whether it will work or not."

"Let's hear it."

"All right. But first, can you manage this plane all right with that bad shoulder?"

"Sure; it's not very bad."

"All right then. Well, you keep under cover about here, moving about just enough to spoil the aim of the foe. I'll drop over the side and swim to the enemy. I can get there un.o.bserved, all right, because they won't be expecting me. I'll pull one of them over and settle with him first. Then I'll get the other."

"I don't know," Frank considered the plan. "I suppose it might work, but there is nothing sure about it."

"There's nothing sure about anything," declared Jack. "But it's better than staying here all the rest of the night. Besides, we must hurry, you know."

"That's right," agreed Frank. "All right, then. So be it. Will you take your gun?"

"No use," said Jack. "It would be wet by the time I got there. Here I go."

"Good luck," Frank called after him.

Gently, Jack lowered himself over the side of the hydroplane, first divesting himself of his coat and shoes; then struck out for the disabled aeroplane.

Slowly the lad swam, for he did not wish to betray his coming by the sound of a splash. The distance was not great and a powerful swimmer, such as Jack, could cover it easily in a few moments.

Jack did not approach the enemy craft from the front. Giving it a wide berth, he swam around it and then, turning quickly, bore down upon the aeroplane more swiftly. He swam with his head barely above the water, and he was ready to dive immediately should he be sighted.

There was not a sound aboard the aeroplane as Jack drew close to it.

Raising his head slightly, he could see no human form.

"Funny," the lad muttered to himself. "Wonder where they keep themselves. No wonder we couldn't hit them."

He was within a few feet of the disabled craft and he now rose higher in the water to get a good look about. Still he saw no one.

Twice around the machine the lad swam and not a human being did he see.

"There is something awfully queer about this," he told himself. "I'll go aboard."

He laid hands on the aeroplane and scrambled aboard. Quickly he sprang to his feet, ready to tackle any foe that might have seen him crawl aboard. Nothing happened.

Jack made a careful inspection of the disabled plane. Then, as he still gazed around, a sudden thought struck him. Without taking time to consider it, he sprang suddenly to the side of the plane and leaped into the water and with swift and powerful strokes struck out for his own craft.

Jack had hit upon the solution of the desertion of the German aeroplane.

Even as Jack had lowered himself from the hydroplane and swam across the water, the Germans in the other craft had done the same thing. Both sides had struck the same plan almost simultaneously. Jack, in making a wide detour as he approached the foes' machine, must have pa.s.sed the two Germans in the water.

Now, realizing that the Germans must be close to the hydroplane, had they not already reached it, and remembering that Frank was wounded, Jack felt a sudden dread steal over him. His long, powerful strokes sent him through the water at great speed.

But the Germans had not made their presence known to Frank yet. Neither was as swift a swimmer as Jack, and for that reason, their progress through the water had been considerably slower. Also they had gone very cautiously.

A short distance from the hydroplane, one had swum to one side of the plane and the second to the other. The Germans also had discarded their revolvers, for they had realized they would be useless after their trip through the water. Also, not being expert swimmers, they had wanted to be unhampered by weight as much as possible.

Frank was still guiding the plane about occasionally to avoid a chance bullet from the enemy, but at the moment the Germans came close, he had stopped the craft and was peering into the darkness, straining his ears for the sound of a struggle that would tell him Jack was engaged with the enemy.

Suddenly a sound came to his ears from across the water, but it was not what he expected, although it was in Jack's voice:

"Frank! Look out! They are after you!"

Instantly, the lad understood the situation. He drew his revolver with his uninjured arm and sprang to one side of the aeroplane. As he did so, a figure reached up and grabbed him by the hand so that he could not fire. At the same time a second figure clambered aboard the craft from the opposite side. Frank raised a cry:

"Hurry, Jack!"

Jack needed no urging. He was swimming through the water as fast as possible.

With a sudden move, Frank jerked his hand loose from the grip that held him and turned just in time to encounter the second German. Frank raised his revolver and fired quickly; but the German ducked, and before Frank could fire again, he had come up close to Frank and grappled with him. In vain Frank sought to release his arm so that he could bring the weapon down on his opponent's head. The man clung tightly.

A sudden lurching of the hydroplane told Frank that the second German was coming aboard. Unmindful of his wounded shoulder, Frank struggled on. With a sharp kick of his right foot he succeeded in knocking the first German's legs from beneath him; and again the lad tried to raise his revolver to shoot the second German, who now advanced.

But the latter was too quick for him. Closing with the lad, the man knocked the revolver from the boy's hand with a quick blow. The weapon spun into the sea.

The first German returned to the attack.

"Get him quick!" he shouted. "There is another one around here some place."

Jack, at this moment, was within a few yards of the boat.

"You bet there is!" he said between his teeth. "And he'll be there in a minute."