With that he dived overboard, at the starboard rail, the side nearest the gunboat. There was a splash--then the waters closed over the machinist.

He came up at about the point he had planned, where he had heard the b.u.mping.

Held below water as he was by the under-hull of the submarine, he could move with certainty, though but slowly.

Groping, the machinist encountered the metal cylinder. Quickly he felt for its connections which, like a flash, he knew must exist. He found the wire, but reached for another. It all had to be done swiftly, for his reserve "wind" was fast giving out. Not finding a second wire, he fastened his nippers against the first wire--then cut. Now, steering the metal cylinder, he pushed it out from under the hull. Cylinder and man rose together.

Whew! What a powerful breath the man took! Then he steered the cylinder carefully against the hull, and managed to hold it there until he could reach a piece of cordage and make the cylinder fast.

This done, he dashed below, thumping hard on the door of the stateroom occupied by Captain Jack Benson and Hal Hastings.

"Eh? What is it?" called Jack, almost instantly.

"You're wanted on deck, Captain--instantly," replied the dripping machinist.

"Oh, all right, Williamson," and Benson's feet hit the stateroom floor.

A minute later he was above, Hal following only some twenty seconds behind his young chief.

Williamson swiftly told how he had heard the b.u.mping against the hull, and how he had found the cylinder, with a wire connection.

"Gunboat, ahoy!" roared Captain Jack, s.n.a.t.c.hing up a megaphone and holding it to his lips.

The response was prompt. In less than three minutes a cutter, containing an officer, a corporal and four marines, was alongside.

"The first thing for us to do is to take that cylinder aboard the 'Waverly' and investigate it," decided Ensign Foss. "I'll leave the marines here until I get further instructions from the commanding officer."

"Anything happening?" demanded Eph, reaching deck just after the cutter had put off. He eyed the marine squad curiously.

"Just what we're trying to find out," replied Jack.

"It must seem to you that I acted amiss in leaving the deck," put in Williamson.

"But you didn't," retorted Jack. "Had you been on deck you wouldn't have heard that infernal machine b.u.mping against the hull."

"Infernal?" echoed Eph Somers, rubbing his eyes. "Say, have I been missing a whole lot by being asleep?"

The other three told him quickly all they knew of what had happened.

Within five minutes the cutter came back, bringing two more marines and a young second lieutenant of that corps.

"Lieutenant Commander Kimball's compliments, sir," reported the second lieutenant. "He will put in an appearance as soon as that cylinder has been investigated. He has sent me with instructions to see what had best be done."

"I don't believe there's much doubt as to what had best be done,"

replied Captain Jack, quickly. "Williamson reports having cut a wire that was attached to that cylinder. I think we can find that wire again, and, if we do, we can easily follow it to its other end."

"By jove, that's good enough," muttered the lieutenant.

"Williamson is already wet," proposed Jack. "He can dive again, and see whether he can pick up that wire. If he needs any help, I'll go overboard with him."

"Wait until I see what I can do," proposed the machinist.

This time he dived over the port side of the craft. Three or four times he came up for air, next going, below again. At last, however, Williamson came up, calling:

"I have a part of the wire in my hands."

Lieutenant Foster ordered his marines into the cutter, inviting Jack and Hal also to go with him. They rowed out alongside of Williamson, picking up the machinist and his wire.

"We'd better put your man back on the boat, hadn't we, Mr. Benson?"

inquired the marine lieutenant.

"I'm not such weak stuff as that, sir," almost grumbled the machinist.

"I can stand a few minutes more in wet clothes, and I want to go along to see where this wire leads."

"Good enough," nodded Lieutenant Foster, he gave the order to row along slowly, while two marines in the bow of the cutter slowly gathered in the wire, at the same time signaling back the direction in which it lay.

Only a few minutes were needed thus to follow the trail straight to the clump of bushes on sh.o.r.e.

"n.o.body leave the boat until we have a lantern ready," directed Lieutenant Foster. "We don't want to tramp out the trail of the rascals who laid that mine."

The marine lieutenant himself was the first to step ash.o.r.e, and Jack Benson was with him.

"Here are the footprints of the rascals," announced Foster, as the two stepped cautiously into the bushes.

"Yes; there were just two of them here, apparently," replied Jack, after studying the prints, and discovering the marks of only two different sizes or kinds of shoes.

"Here's the imprint of a box," added Foster. "Good heavens, the scoundrels had a regular magneto battery, insulated wire and all, for firing that mine from the sh.o.r.e. Mr. Benson, they meant to blow your boat into Kingdom Come!"

"It looks that way," replied Jack Benson, composedly.

On hearing that voice, so even and unaffected in its utterance, Lieutenant Foster looked at the submarine boy keenly.

"By Jove, Benson, you're cool enough to be an admiral," muttered the marine officer, admiringly.

"Why, this doesn't seem to be a joke on me," replied Captain, Jack, smiling back at the lieutenant.

"A joke!"

"It's one on the Secret Service," laughed Jack, quietly. "They are the ones who are supposed to have the job of keeping off spies and all of their kind."

"Yes; this certainly came from the spies, or their friends," muttered Lieutenant Foster. "Jove, but we have a desperate crowd to deal with when they'll go to such a length as this in time of peace!"

"Oh, it may all turn out to be a joke," put Hal, quietly. "Some one may have been doing this to try us out. That metal cylinder may prove to have been loaded with ginger-bread or peanuts. If anyone has been trying a joke on us, then I'm mighty glad we didn't get rattled."

"I reckon we shall soon know just what that cylinder did contain,"

muttered Lieutenant Foster. "Here's another cutter coming from the 'Waverly,' and I think I make out Lieutenant Commander Kimball in the stern-sheets."

It was, indeed, the lieutenant commander. As he stepped ash.o.r.e, his face coming into the circle of light cast by the lantern, his features were seen to be white with anxiety.