For several days after that Darrin and the “Logan” cruised back and forth over the area assigned for patrol. During these days nothing much happened out of the usual. Then came a forenoon when Darrin received a wireless message, in code, ordering him to report back at once to the commanding officer of the destroyer patrol.

Mid afternoon found the “Logan” fifteen miles off the port of destination.

“Be on the alert every instant,” was the order Darrin gave out to officers and men. “There have been several sinkings, the last month, in these waters. We are nearing Fisherman’s Shoal, which is believed to be a favorite bit of ground for submarines that hide on the bottom.”

Over Fisherman’s Shoal the water was only about seventy feet in depth—an ideal spot for a lurking, hiding undersea craft.

Five minutes later the bow lookout announced quietly:

“Trail of bubbles ahead, sir.”

Leaving Ensign Phelps on the bridge, Dave and Dan darted down and forward.

A less practised eye might have seen nothing worth noting, but to the two young officers the trail ahead was unmistakable, though Darrin quickly brought up his glass to aid his vision.

“Pass the word for slow speed, Mr. Dalzell,” Dave commanded, quietly. “We want to keep behind that craft for a moment. Pass word to Mr. Briggs to stand by ready to drop a depth bomb.”

Quietly as the orders were given, they were executed with lightning speed. The destroyer began to move more slowly, keeping well behind the bubble trail. At any instant, however, the “Logan” could be expected to leap forward, dropping the depth bomb at just the right moment. Then would come a muffled explosion, and, if the bomb were rightly placed, a broad coating of oil would appear upon the surface.

Dave was now in the very peak of the bow. Watching the bubbly trail he knew that the hidden enemy craft was moving more slowly than the destroyer, and he signalled for bare headway. And now the bubbles were rising as though from a stationary object under the waves.

“Buoy, there!” he ordered, quickly. “Overboard with it.”

Slowly the destroyer moved past the spot, but the weighted, bobbing buoy marked the spot plainly.

“Have a diver ready, Mr. Dalzell,” Dave called. “Make ready to clear away a launch!”

In the matter of effective speed Darrin’s officers and crew had been trained to the last word. Only a few hundred yards did the “Logan” move indolently along, then lay to.

Soon after that the diver and launch were ready. Dave stepped into the launch to take command himself.

“May I go, too, sir?” asked Dan Dalzell, saluting. “I haven’t seen this done before.”

“Clear away a second launch, Mr. Dalzell. The crew will be armed. You will take also a corporal and squad of marines.”

That meant the entire marine force aboard the “Logan.” Dalzell quickly got his force together, while Darrin gave orders to pull back to where the bobbing buoy lay on the water.

“Ready, diver?” called Dave, as the launch backed water and stopped beside the buoy.

“Aye, aye, sir.” The diver’s helmet was fitted into position and the air pump started. The diver signalled that he was ready to go down.

“Men, stand by to help him over the side,” Darrin commanded. “Over he goes!”

Hugging a hammer under one arm the diver took hold of the flexible cable ladder as soon as it had been lowered. Sailors paid out the rope, life line and air pipe as the man in diver’s suit vanished under the water.

Down and down went the diver, a step at a time. The buoy had been placed with such exactness that he did not have to step from the ladder to the sandy bottom. Instead, he stepped on to the deck of a great lurking underseas craft.

He must have grinned, that diver, as he knelt on top of the gray hull and hammered briskly, in the International Code, this message to the Germans inside the submarine shell:

“Come up and surrender, or stay where you are and take a bomb! Which do you want?”

Surely he grinned hard, under his diver’s mask, as he noted the time that elapsed. He knew full well that his hammered message had been heard and understood by the trapped Huns. He could well imagine the panic that the receipt of the message had caused the enemy.

“We’ll send you a bomb, then?” the diver rapped on the hull with his hammer. “I’m going up.”

To this there came instant response. From the inside came the hammered message:

“Don’t bomb! We’ll rise and surrender!”

Chuckling, undoubtedly, the diver signalled and was hoisted to the surface. The instant that his head showed above water the seaman-diver nodded three times toward Darrin. Then he was hauled into the boat, and the launch pulled away from the spot.

“It took the Huns some time to make up their minds?” queried Dave Darrin smilingly, after the diver’s helmet had been removed.

“They didn’t answer until they got the second signal, sir,” replied the diver.

Dalzell’s launch was hovering in the near vicinity, filled with sailors and marines, a rapid-fire one-pounder mounted in the bow.

Both boats were so placed as not to interfere with gun-fire from the “Logan.” Officers and men alike understood that the Huns might attempt treachery after their promise to surrender.

Soon the watchers glimpsed a vague outline rising through the water. The top of a conning tower showed above the water, then the rest of it, and last of all the ugly-looking hull rose until the craft lay fully exposed on the surface of the sea.

The critical moment was now at hand. It would be possible for the submarine to torpedo the destroyer; there was grave danger of the attempt being made even though the vengeful Germans knew that in all probability their own lives would pay the penalty.

The hatch in the tower opened and a young German officer stepped out, waving a white handkerchief. He was followed by several members of the crew. It was evident that the enemy had elected to save their lives, and smiles of grim satisfaction lighted the faces of the watchful American jackies.

“Give way, and lay alongside,” Dave ordered his coxswain, while signalling Dalzell to keep his launch back for the present.

Then Dave addressed the young German officer:

“You understand English?”

“Yes,” came the reply, with a scowl.

“We are coming alongside. Your officers and men will be searched for weapons, then transferred, in detachments, to our launch, and taken aboard our craft.”

The German nodded, addressing a few murmured words to his men, who moved well up forward on the submarine’s slippery deck.

As the launch drew alongside two seamen leaped to the submarine’s deck and held the lines that made the launch fast to it.

Half a dozen armed seamen sprang aboard, with Darrin, who signalled to the second launch to come up on the other side of the German boat.

“Be good enough, sir, to order the rest of your men on deck,” Dave directed, and the German officer shouted the order in his own tongue. More sullen-looking German sailors appeared through the conning tower and lined up forward.

“Did you command here?” Dave demanded of the officer.

“No; my commander is below. I am second in command.”

Dave stepped to the conning tower, bawling down in English:

“All hands on deck. Lively.”

Another human stream answered. Darrin turned to the German officer to ask:

“Are all your crew on deck now?”

Quickly counting, the enemy officer replied:

“Yes; all.”

“And your captain?”

“I do not know why he is not here. I cannot give him orders.”

By this time the marines were aboard from the second launch. Already the first detachment of German sailors, after search, was being transferred to the launch.

“Corporal,” called Darrin, “take four men and go below to find the commander. Watch out for treachery, and shoot fast if you have to.”

“Aye, aye, sir,” returned the corporal, saluting and entering the tower. His men followed him closely.

“I’ve seen the outside of enough of these pests,” said Dave to his chum. “Suppose we go below and see what the inside looks like. The German submarines are different from our own.”

Dalzell nodded and followed, at the same time ordering a couple of stalwart sailors to follow. A boatswain’s mate now remained in command on the submarine deck.

“You get back there!” growled the corporal. Dave reached the lower deck just in time to see the corporal pointing his revolver at a protesting German naval officer.

“Look what he’s been doing, sir,” called the corporal. “Look on the floor, sir.”

On the deck lay a heap of charred papers, still smoking.

Charred papers still smoking.