The two returned on deck.

The day passed quietly.  No submarines were sighted, and at last the flotilla reached the point where the destroyers were to leave the homeward bound transports to pursue their voyage alone.  The transports soon grew indistinguishable, almost, in the semi-darkness.  The senior naval officer aboard the Plymouth hoisted signal flags.

“Bon Voyage,” they read.

Through a glass Jack read the reply.

“Thank you for your good work.  Best of luck.”

From the S.N.O. (senior naval officer) came another message.  Frank picked it up.

“Set course 188 degrees.  Keep lookout for inbound transports to be convoyed.  Ten ships.”

Again the destroyer swung into line.  It was almost seven o’clock—­after dark—­when the lookout aboard the Plymouth reported: 

“Smoke ahead!”

Instantly all was activity aboard the destroyers.  Directly, through his glass, Jack sighted nine rusty, English tramp steamers, of perhaps eight thousand tons, and a big liner auxiliary flying the Royal Navy ensign.

Under the protection of the destroyers, the ships made for an English port.  The night passed quietly.  With the coming of morning, the flotilla was divided.  The Plymouth stood by to protect the big liner, while the other three destroyers and the tramp steamers moved away toward the east.

“This destroyer game is no better than driving a taxi,” Frank protested to Jack on the bridge that afternoon.  You never see anything.  I’d like to get ashore for a change.  I’ve steamed sixty thousand miles since last May and what have I seen?  Three ports, besides six days’ leave in London.”

“You had plenty of time ashore before that,” replied Jack.

“Maybe I did.  But I’d like to have some more.  Besides, this isn’t very exciting business.”

Night fell again, and still nothing had happened to break the quiet monotony of the trip.  Lights of trawlers flashed up ahead.  Interest on the bridge picked up.

“Object off the port bow,” called the lookout.

“Looks like a periscope,” reported the quartermaster.

Frank snapped his binoculars on a bobbing black spar.

“Buoy and fishnet,” he decided after a quick scrutiny.

Frank kept the late watch that night.  At 4 a.m. he turned in.  At five he climbed hastily from his bunk at the jingle of general alarm, and reached the bridge on the run in time to see the exchange of recognition signals with a British man-o’-war, which vessel had run into a submarine while the latter was on the surface in a fog.  The warship had just rammed the U-boat.

“Can we help you?” Frank called across the water.

“Thanks.  Drop a few depth charges,” was the reply.

This was done, but nothing came of it Frank returned to his bunk.

“Pretty slow life, this, if you ask me,” he told himself.

He went back to sleep.