Dave's eyes gleamed as he made out the next signal from the patrol, which was:
"Soundings show her to be a big craft. Shall we rig the small bombs on the sweep wires?"
"Wait until we arrive," was the answering signal from the "Grigsby."
In a few minutes the destroyer was within hailing distance of the patrol boat, which was lying to in the neighborhood of the find.
"The enemy submarine appears to be at least 275 feet long, sir," reported the patrol boat commander.
"Then a depth bomb should do the business better," Dave shouted back through the megaphone. "Sail over the craft with your sweep, and I'll follow. Signal when you judge us to be squarely over her."
Under bare headway the "Grigsby" fell in behind the now slow-moving patrol boat. Almost at once the wire sweeps discovered the hull of the hiding monster.
Ahead steamed the patrol boat, the destroyer following. Aft two men stood by the depth bomb apparatus. Down came the white flag of the British signalman on the smaller craft.
Dave's hand rested on the telegraph lever to the engine-room. He signalled for full speed ahead, then at the proper moment he shouted:
"Let her go!"