Again Kapitan Schwalbe smiled broadly.
"No," he replied. "There is no need. Cases of illness must wait till we return to port. The only injuries we are likely to sustain would put us beyond all medical aid. But several of the men are fairly skilled in rough surgery, so I will——"
"Vessel on the port bow, sir; she's showing no lights," announced a voice.
"All hands to stations!" ordered the skipper.
"Down below with you!" hissed the petty officer, who during the interview had stood rigidly at attention at two paces to the rear of his charges.
Already the hitherto recumbent men were alert. Quickly, yet in order, they disappeared down the fore hatchway, and amongst them were Ross and Vernon.
The officers had taken their places inside the shelter of the conning-tower. Everything was battened down from within, and with a gentle purr the electric motors were set in motion, while at the same time water ballast was admitted into the trimming-tanks.
Swift and stealthy had been their preparations, but the presence of the submarine was betrayed by the phosphorescent swirl of the water caused by the churning of the twin propellers as she slipped beneath the surface.
Twenty seconds later a swift vessel that looked suspiciously like a trawler, although her speed belied her, tore over the place where U75 had disappeared. Bare inches only separated the top of the latter's conning-tower from the massive keel plates of the craft that had all but accomplished its mission.
The watch-dogs of the British Navy were at work.