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."