but one. A deck of cards decided who was to stay, and Jack had drawn the fatal card—the ace of spades.

Officers and crew were launched to safety by means of a torpedo tube; and Jack sat down to await the end. But, in some unaccountable manner, the submarine had suddenly risen to the surface, and Jack, taking advantage of the single instant the vessel was above water before it took its final death plunge, flung himself clear. And thus all were saved.

But, because of their desperate experiences, they were unfit to immediately resume new duties; so all had returned to England until such time as they would be physically in shape again.

Now Jack Templeton, although young in years, was wise in the ways of the world. Also he was of huge stature and as strong as an ox, as he had proved more than once when put to the test. Frank, although by no means as large as his chum, was sturdy and strong, and able to give a good account of himself when occasion required.

The one noticeable difference between the two was that Frank was high-tempered and quick, whereas Jack was always cool and collected. And this very fact had more than once showed that Jack, while not exactly more dependable, could always be relied upon to keep his head.

While both were skillful in the use of weapons, here was a place where Frank excelled. He was a dead shot with rifle or revolver and was a strong swordsman. Jack was a good shot himself and a skillful fencer, but he was not in Frank's class when it came to the use of sword or firearms.

Upon their last expedition Jack and Frank had acted as first and second officers respectively of the submarine, and both now held the rank of first lieutenant. Their promotions had come deservedly. They had the implicit confidence of Lord Hastings and more than once had offered valuable advice, which Lord Hastings had acted upon.

Now a few words about the progress of the war. The seven seas had for some time, save for the presence of the German submarines, been swept clear of German, Austrian and Turkish fighting ships. Not a one remained at large to prey upon the shipping of the Allies. The real fighting strength of the navies of the three central powers still remained in their own fortified bases, well guarded by mines.

The Allies had established such an effective blockade that none dared to venture forth. So the naval situation was practically at a standstill, where indications pointed to its remaining until the main German fleet, bottled up in Heligoland, and the main Austrian fleet in the Adriatic should summon sufficient courage to sally forth and give battle; and there had been nothing to indicate any sudden action on the part of either.

On several occasions British submarines had penetrated the mine fields and created considerable havoc, and aircraft had dropped bombs from the air. But along these lines the German submarines had been more successful and now were the one real menace confronting the naval supremacy of the Entente powers.

Hundreds of ships, large and small, had fallen easy prey to these under-sea terrors. Big ocean liners, crowded with passengers, non-combatants, had been sent to the bottom with terrible loss of innocent lives. Chief among these tragedies laid to the door of the German submarines was the sinking of the Cunard liner Lusitania, in which more than a thousand men, women and children had been drowned.

And, so far as the British public knew, England had taken no steps to combat this under-sea peril. However, as Lord Hastings had told the boys at the opening of this story, Great Britain had taken such steps, and that they were effective was evident from his additional statement that in the neighborhood of a hundred submarines had "vanished."

But this warfare was not to end until the submarine evil had been eradicated. The German under-sea craft must be disposed of so effectively as to preclude further danger to British shipping. And it was in this work that Jack and Frank were soon to play a prominent part.

CHAPTER II.

ON ACTIVE SERVICE AGAIN.

For some reason unknown to Jack and Frank, when morning came, Lord Hastings announced that the start would not be made until after nightfall, at which both lads showed keen disappointment.

"I'll tell you what you can do," said Lord Hastings. "I'll give you an order for my motorboat and you can go to Gravesend during the day if you care to. I'll meet you there at the Lion Inn to-night at 10 o'clock."

Frank was delighted.

"That's better than hanging around here all day, waiting for night to come," he said. "What do you say, Jack?"

"Anything to humor you," replied the latter with a smile.

"Take all your things with you," said Lord Hastings; "and, above all, hang on to that motorboat. Don't let anybody get it away from you."

"We'll hang on to it, never fear," replied Frank. "Come on, Jack."

"Wait a minute," ordered Lord Hastings. "You'll need this written order to get the boat."

"I'd forgotten, sir," said Frank.

Lord Hastings scribbled rapidly on a piece of paper, which he passed to Jack.

"This will fix you up," he said. "Now remember, 10 o'clock sharp."

The boys nodded their understanding of this order, saluted and left. Getting their things together, they hurried to the river, where Lord Hastings kept his motorboat; and an hour and a half later they were proceeding slowly down the river.

"Guess none of the enemy will ever get in here," declared Frank, after a careful survey of the river.

"Guess not," replied Jack. "Look at the boats. You wouldn't think we were at war."

"Not if it wasn't for the warships," agreed Frank. "And there are enough of them to make it hot for any hostile fleet. But it's a wonder to me some of these German submarines haven't taken a little trip up the Thames."

"Mines," replied Jack briefly.

"True," said Frank, "but you will remember we took a pretty long jaunt up the Dardanelles, and passed through the Kiel canal."

"And when you stop to think of it, we're pretty lucky to be here right now," returned Jack dryly.

"Well, so we are, if that's the way you look at it. However, I wouldn't mind having another such chance."

"You'll probably get it."

Conversation lagged as the boys took in the scenes about them; and there was little more talk during the trip. They stopped more than once, and, loitering along, it was dark when they neared their destination.

As they would have drawn up to the wharf there was a sudden flash of light—gone in a moment—followed by a dark body that swished by them like a flash.

Frank uttered an exclamation of astonishment.

"See that?" he demanded.

"Yes. What could it have been?"

"You've got me, but it's heading toward the open sea. Great Scott! Maybe it's an enemy."

"An enemy?"

"Yes; you know how anxious the Germans are over this submarine business. Maybe this fellow has been spying about. May be going to report to a German submarine out there some place."

"Think we had better follow and have a look?" asked Jack.

"Believe it would be a good idea. Let's go."

Without another word, Jack brought the boat about and headed after the one that had so recently dashed by them. In the darkness ahead there was nothing to be seen.

"Like looking for a needle in a haystack," Jack called to Frank.

"That fellow can't be up to any good," declared Frank. "He showed no light and was going in a terrible hurry. There's something up."

"Does seem that way," agreed Jack.

"Say! Is this as fast as this thing can go?" demanded Frank. "We won't ever get any place this way. Let her out a bit."

Jack did so and the little boat seemed literally to fly over the dark water. This terrific speed Jack kept up for some time and then slowed down.

"We'll bump into something at this rate," he said; "and that would settle the whole