"Again we 'canned' him, and again the thickening trail of grease gave promise that, if nothing else, we were at least bleeding him hard, perhaps to death. As there was no doubt that he was still a going concern, however, the captain decided on a change of tactics, to try attrition, so to speak, instead of direct assault. "There is, of course, a limit to the number of 'cans' a destroyer can carry, and those which still remained he wanted to husband against a better chance to use them with effect. The several remaining hours of daylight would be enough, if the U-boat could be kept running at maximum speed, to exhaust its batteries in and force it to come to the surface for lack of power to keep going submerged. A submarine, you understand, unless it can lie on the bottom, which was impossible here on account of the depth, must keep under weigh to maintain its bouyancy, so it follows that the exhaustion of its batteries leaves no alternative but coming up. That was what we were now driving at with this one. "About this time, hearing the radio of the _Cushman_ close aboard, the captain sent a signal requesting her help in clearing up the job in hand. She hove in sight presently, accompanied by the _Fanny_, which was out with her on some special stunt of their own. They had an hour to spare for us, and in that time we played just about the merriest little game of hide-and-seek that any of our destroyers have had with a Fritz since the Yanks came over. "He wasn't left time to sit and think for a single minute. Now a destroyer would come charging up his wake from astern and shy a 'can' at his tail; now one would ambush him from ahead and try and have one waiting where his nose was going to be. "It was a good deal like when three or four of us kids used to spear catfish in a muddy pool. We were always grazing one, but never quite getting it. And, believe me, the wake of one of those catfish didn't have anything on the wake of that Fritz for sinuosity. "He was zigzagging constantly, and just after charges had been dropped on him he twice broached surface. It was only for a few seconds though, and never long enough to offer a target for even a ranging shot. Once we tried to ram, but he turned as he submerged, and the forefoot cut into nothing more solid than his propeller swirl. [Illustration: A LIMIT TO THE NUMBER OF "CANS" A DESTROYER CAN CARRY] "After the _Cushman_ and _Fanny_ left us to resume their own job the _Sherill_ took up the chase again on her own account. There were still about three hours to go till dark, and two of these we spent in keeping our quarry on the jump by every trick we knew. Then we stood away, and gave him a chance to come up and start charging on the surface. When it finally became evident that he was not going to take advantage of our consideration on this score, we closed in again, picked up his wake, sent down another 'can' or two to tell him what we thought of him.