It occurred to me that the air was escaping through the vents with a strangely loud noise, but before I could consider the matter further or even inquire the reason for this sudden dive, the noise increased to a terrifying extent, and whilst I prepared myself for the worst it culminated into a roar as of fifty express trains going through a tunnel, mingled with the noise of a high-powered aeroplane engine. The roar drummed and beat and shook the boat, then died away as suddenly as it came; a moment later there was a severe jar. We had struck the bottom, still maintaining our angle. I painfully got to my feet and then discovered from the navigator that he had suddenly seen two white patches of foam 800 yards on the starboard bow, which resolved themselves into the bow waves of a destroyer approaching at full speed to ram. We had dived just in time, and her knife-edged bow, driven by 30,000 horse power, had slid through the water a very few feet above our conning tower. Luckily he had not dropped any depth charges. We were not, however, completely free of our troubles, though we had cheated the destroyer. Examination of the chart, showed the bottom to be mud, and on attempting to move the foremost hydroplanes, the plane motor fuses blew out. This showed that the boat was buried in the mud right up to her foremost planes, which were immovable. The hydrophone watchkeeper reported that he could still hear fast-running propellers, though probably some distance away, and as this showed that our old enemy was still nosing about we were very anxious not to break surface. We just blew "A." [1] At least we started to blow "A," but Alten wisely decided that, as it was a calm night with a half-moon, the bubbles on the surface might be rather conspicuous, so we stopped the blow and put the pump on. We also flooded "W". [2] This had no effect on her at all. [Footnote 1: Probably their foremost internal tank.--ETIENNE.] [Footnote 2: Presumably their after internal tank.--ETIENNE.] We then pumped out "Q" and "P," leaving "W" full, and adjusted our trim to give her only three tons negative buoyancy, just enough to keep us on the bottom if she came out of the mud. In this position we went full speed astern on the motors, 1,500 amps on each, and all the crew in the after-compartment. No result. We then pumped the outer diving tanks on the port side to give her a list to starboard. Still she remained fixed. So at 2 a.m. we decided to risk it and we put a slow blow on all tanks.