Perhaps the only four men with the fleet who did not really have their interests aroused were Davis and his three fellow conspirators.  Their only hope was that the sooner they came through the venture successfully the sooner they might get to work on their own plans.

The submarine fleet sped silently through the waters, going as swift as the wind; and when it finally reached the broad mouth of the Thames, the key to London itself, it still lacked two hours of dawn.  But it was time for quick work and Admiral Schuler was not the man to hesitate—­had he been, he would not have held this important post.

The submarines came to the surface now, in accordance with previous instructions, and Admiral Schuler, by a signal with his light, instructed the U-16 to proceed ahead.  The other vessels dropped back a little.

“Well,” said Lord Hastings to Frank and Jack, who stood beside him on the bridge, “here goes.  May good fortune attend us.”

He gave Jack the command: 

“Full speed ahead!”

CHAPTER XX.

THE TRAP IS SPRUNG.

As the three officers aboard the U-16 knew, British battleships and vessels of war of all descriptions had been stationed all along the Thames, many of them patrolling the very mouth of the river.  But now, as Lord Hastings, Jack and Frank stood upon the bridge of the little submarine after it had entered the mouth of Thames, there was not a vessel of any kind to be seen in the darkness.

“Admiral Fischer’s orders have been followed out, sir,” said Jack in a low voice.

Lord Hastings nodded but made no reply.

Behind the U-16 the other German submarines followed closely, two abreast.  Aboard each the men stood to their posts, awaiting the signal they expected at any minute.  All the vessels moved along upon the surface.  The officers, from their places upon the bridge, followed with their eyes the movements of the U-16, which displayed a small stern light to guide them on.

In case of danger Lord Hastings had been instructed to give immediate warning, that the vessels behind might have time to dive.

Perhaps a hundred yards away in the darkness Frank’s keen eyes now made out the forms of many little craft approaching them silently and swiftly.  He immediately called Lord Hastings’ attention.

“The motorboats,” replied the latter quietly.  “Things are working out just right.”

Behind the motorboat flotilla could be seen forms of larger and mightier ships of war—­the torpedo boats which were advancing in the wake of the mosquito fleet to surround the enemy submarines and capture or sink them.  They came along close to the shore on either side of the river and the U-16 continued up the river in the exact center.

“When we get by, they’ll close in,” said Lord Hastings.

But now one of the commanders with the motorboat flotilla could restrain his impatience no longer, and while still some distance from the enemy gave the command to fire.