"What's the dope?" asked Billy, with great interest. "Suppose he does spot one, what good does it do?"
"He's got a wireless equipment," explained Frank, "and he sends out signals to trawlers and destroyers. They come on the jump and the seaplane tells them just where the submarine is lying."
"By jiminy, I think he sees one now!" exclaimed Tom Bradford, who had just come up. "See that smudge of smoke over there? That means a steamer's coming and there's another."
As though by magic one boat after another hove in sight until there were four, coming from as many points in the compass and heading toward that point in the sea over which the seaplane hovered.
The boys were on edge with excitement at the prospect of being in at the death and as the liner was rapidly approaching the scene of action, they had a clear view of what followed.
Guided evidently by signals from the seaplane, two of the trawlers stretched a long chain between them and advanced slowly toward the other two who, with a similar chain approached from the other direction.
"What do you suppose they're trying to do?" asked Billy, curiously.
"The idea is, to get those chains under the submarine," explained Frank. "After they've done that, they'll crisscross them from above. If they once succeed in doing it the sub is done for. He's got to come up and surrender or else they'll slip him a depth bomb and blow him to flinders."
Deftly and quickly the work went on under the direction of the skilled veterans who held command of the trawlers. Then they waited for the submarine to come up.
But it did not come. Instead, it released a group of mines on the chance of wrecking one or more of its captors. But they were on the lookout for just such a contingency and fended off these "floating deaths," waiting till they had finished their more important work before rendering them harmless.