Just as Donald, who was no match physically for the burly machinist, was pondering what to do, the door which was open became filled by a rotund figure.

It was Tubby.

In a jiffy he took in the scene, the threatening att.i.tude of Barton, the alarmed look of Donald, who stood staring at the revolver like a bird fascinated by a snake. Tubby realized that it was no time for thinking the situation over. Instead, he crouched low, and then, darting forward with surprising agility, he seized the machinist around the legs before the fellow knew what was happening.

Taken utterly by surprise, and borne off his feet by Tubby's rush, Barton came crashing to the floor in a heap. As he fell the revolver exploded, the bullet pa.s.sing by Donald's head.

Barton struggled desperately with Tubby, but the stout youth held on to him like a leech, at the same time yelling for help. In a few seconds the ensign and Mr. Barr came rushing in, followed by the Boy Scouts and the sailors. There was an end to the battle then and there. After a brief resistance Barton, snarling and cursing, was tied hand and foot, and the ensign ordered him locked up in the dining room shed for the present.

Donald soon told his story and proudly exhibited the message from the air which told of sighting the green motor boat. All agreed that it was a cheering bit of news.

"If they were near a lot of islands when sighted, it is most probable that they are hiding on one of the group. At all events, having the lat.i.tude and longitude, it will be easy to go down there and see."

"What are you going to do about Barton? We have full proof of his villainy now," struck in Merritt.

"I suppose we shall have to take him along with us. We can't waste time going ash.o.r.e now and risking the law's delays. We will go down the coast in the submarine with the _Viper_ acting as escort, and Barton a prisoner on the _Peacemaker_," decided the ensign.

"I wonder why he was so anxious to see that message?" spoke Tubby.

"I guess he knew we were trying to trace the green motor boat, and was watching the wireless through that window. When he saw Donald busy taking a message, he guessed what it was, and decided that it was necessary for him to see it," hazarded Mr. Barr. "How I have been deceived in the rascal!"

"You certainly have. His actions show him to be a scoundrel of the worst type," agreed the ensign.

There was not much more sleep for anybody that night. Excitement ran far too high for that. An attempt was made to force Barton to confess his part in the conspiracy, but he sullenly refused to talk.

"You've got nothing on me," was all he would vouchsafe. "Anything those tin soldier kids tell you is patched up out of whole cloth."

Slumber being out of the question, the rest of the night was devoted to stocking both craft with food and water in good quant.i.ties. In this work the Scouts helped with a will. They were aided by the three sailors, who were to be left behind to guard the island, and therefore did not work any too hard.

Dawn found all in readiness, and at the summons of the bugle all lined up before Ensign Hargreaves to receive their orders. To the submarine were a.s.signed Merritt and Donald, besides Mr. Barr, Ensign Hargreaves, and the prisoner Barton. The _Viper's_ crew was captained by Tubby, a capable motor boat engineer, and Hiram and the others. When this had been done, Barton was led before Ensign Hargreaves.

"Barton," said he sternly, "you have acted the part of a scoundrel and should be behind the bars now. But I need you for work, and upon the manner in which you perform it, will depend just how severe your punishment will be. Cast him loose, men, and take him into the engine room of the submarine. You are to stand by for orders."

"I'll try to do my best, sir," rejoined Barton in a soft tone of voice, very unusual for him. "I'm sorry, sir, for what I did, but I was led astray by promises of money."

This change in the man was almost startling. From a sullen, morose fellow he had suddenly, or so it seemed, become a dutiful, attentive man, willing to obey orders and do his best. Was all this genuine? We shall have to go further to see.

There being no excuse for delay, and as all were anxious to get off as quickly as possible, the two craft were boarded. The hatch of the submarine was left open for the present, for it was the intention of the ensign to run "awash," as it is called.

The motor boat running very nearly as fast as the submarine, they kept each other company down the coast with little difficulty. It was fine, exciting sport in the motor boat as it cut its way over the swells, hurling spray and water out to either side of its sharp bow. If only the boys had had Rob with them, they would have enjoyed it much more, though.

All that was visible of the submarine was the top of her conning tower, and the slender, needle-like "eye" of the periscope. The water surged round her conning tower as she rushed along, for all the world like some sea monster speeding on an errand of destruction. She was not going full speed, for the ensign wished to keep company with the motor boat.

At noon, just as the lads on the motor boat were settling down to lunch cooked on a blue-flame stove, a head was thrust out of the conning tower. It was that of Mr. Barr.

"We are going to run under the surface in a short time," he said; "just follow your same course, and you'll pick us up when we rise again."

"All right," shouted Tubby, his mouth full of ham sandwich, which he held in one hand, while with the other he clasped a big wedge of pie.

The hatch on top of the conning tower closed shortly after with a metallic "clang." The next instant the craft vanished from view in a swirl of water. For a time the tip of the periscope tube, which was twenty-five feet long, projected above the surface; then that, too, vanished, and the motor boat was alone on the ocean.

On board the submarine the lads were enjoying themselves as much as their fellow Scouts on the motor boat. This second experience was even more novel and enjoyable than their first dive. Mr. Barr sat in the cabin reading some scientific works. Barton, seemingly a changed character, was at work in the engine room. The negro cook was in the galley, while in the conning tower the ensign was giving Donald and Merritt a lesson in handling a diving craft.

In fact, it was Merritt who was at the deflecting apparatus when the occupants of Tubby's boat saw the submarine sink.

"That is the descending lever and this the ascending one," explained the officer before Merritt sent the boat under the surface.

The levers were small affairs and looked fragile for the work they did of starting up the mighty pumps that caused the boat to rise or sink at will.

"What if one of them should break or be lost?" asked Donald.

"Well, if we were under water and the ascending lever happened to be missing, we should be in an awkward position, and I don't believe that Mr. Barr carries an extra one."

"Gracious! Then if the lever was lost we should have to stay at the bottom of the sea?"

"That's about the size of it," was the reply.

Mr. Barr, coming into the conning tower just then, confirmed the officer's suspicion that no extra lever was carried.

"I admit there ought to be one as a matter of precaution," he said, "but we were in such a hurry to give the boat her tests that we forgot about it."

All the afternoon the submarine ran under the water, rising about sunset to the surface. In the distance was the motor boat, but far in the rear.

The _Peacemaker_ was sent around in circle and soon came alongside her companion craft.

Then the hatchway was opened and the ensign shouted some orders to Tubby. The submarine was going to dive once more, but would come up before dark. When night fell a red light would be carried astern which the motor craft was to follow throughout the night. When this had been made clear, the _Peacemaker_ dived once more, but this time it had been decided to send her down to a good depth.

"We will eat an early supper under water just for the novelty of it,"

declared Mr. Barr.

While the meal was going forward Barton was sent into the conning tower to navigate the craft. He obeyed with the same smooth complacence with which he had received every order since his attack on Donald. Evidently the man was hoping, by good behavior, to save himself from a long jail sentence.

After supper Barton was relieved, and Merritt sent to the wheel in his place. He had been in the conning tower but a short time when he was joined by Ensign Hargreaves and Mr. Barr.

"I guess we'll go to the surface now," said the inventor; "it must be almost dark up above."

Merritt reached for the lever that operated the ascending pumps. Right then he received the most acute and alarming shock of his life.

There was no lever there!

"It's gone!" he shouted.

"What? What's gone?" repeated the inventor in a puzzled tone.

"The lever! The ascending lever! We can't rise to the surface without it."

The inventor turned pale. Drops of sweat stood out on his forehead. Even the ensign turned a shade whiter than usual.

If the lever could not be discovered, they were doomed to an awful death in the depths of the sea!