And are these external tubes water-tight? Theoretically, yes, but what of practice? We have been down to forty metres several times during this trip, and not once have we had a chance on the surface of getting at the two external tubes; add to which our depth gear, with the pivots of the weight exposed to water if the tube does flood and then you have rust, corrosion and heaven knows what complications. I saw a British Mark 11.50 torpedo at the torpedo shop at Bruges the other day, and I was much struck with their deep depth gear, which is of the unrestrained Uhlan type, i.e., weight and valve interdependent. But then the main feature is that the whole gear is contained in a separate water-tight chamber. Our system is certainly a great saving in space, and is much neater in design, whilst I prefer the Uhlan principle of valve conjuncting with weight, but it would be interesting to know whether the British have much trouble with the depth-keeping of their torpedo. I have written quite a disquisition on depth gears; I must get on with my record of events. After lunch we had a good look round, but the small airship was still hanging about, flying slowly in large circles. We were rather surprised to meet one of these despicable little sausages or "Zeppelin's Spawn," as the navigator calls them, so far from land, and at dark we surfaced and proceeded on one engine on an easterly course, charging the battery right up with the other engine. Dawn revealed a blank horizon, not a vestige of mast, funnel or smoke in sight. We ambled along in fine though cold weather, and I took advantage of the peacefulness of everything to do a really good series of Müller on the upper deck, stripped to the waist, and allowed the keen air to play its invigorating currents on my torso. Alten silently watched me from the conning tower, with a sneering expression on his face. The navigator, who is quite a decent youngster, though of no family, was, I could plainly see, struck by my development, and asked to be initiated into the series of exercises. I agreed willingly enough to show them to him. I will confess I wish Zoe could have seen me as I perspired with healthy exercise. At about 11 a.m. a couple of masts, then two more, then another, appeared above the horizon. The visibility was extreme, so we at once dived and proceeded at full speed, ten metres. We had been going thus for perhaps half an hour when Alten remarked that he would have another look at the convoy. We eased speed, came up to six metres, and Alten proceeded up into the conning tower to use "A" periscope. He had hardly applied his eye to the lens when he sharply ordered the boat to ten metres, accompanying this order with another to the motor room demanding utmost speed (_Ausserste Kraft_). I went up to the conning tower and found him white with excitement.