On drifting patrol 15 miles South of St. Catherin's light, Isle of Wight, the Aylwin had been circling vicinity for two hours, after dusk had just gone out of Hydrophone range when an enemy submarine broke water within two boat's lengths of starboard quarter of S.C. #143. Evidently ballast tanks had been blown without using propellers, which started when conning tower was up, promptly reported by "C" tube listener on #143, which fired Y-gun immediately before getting underway. Submarine was distinctly visible to all hands on deck of the #143. On starting 143 dropped two more charges from stern, ordering #177 to stand by, but not to move. #143 circled and stopped, at once reporting that submarine was approaching her starboard beam on the surface close aboard, apparently being unable to dive. When within estimated range "Y" gun was again fired by 143 underway, and another charge, set 50 ft., dropped from stern across estimated course of enemy. Submarine submerged - night dark - 143 anchored. S.C.#177 drifted so that one boat would be near submarine whatever it did. Tubes down, and for an hour listened to hammering and other sounds, like fuses blowing out, from submarine. Also heard his anchor chain pay out. Then S.C.#177 anchored. After getting very accurate cross bearings, #177 attacked estimated spot with four charges, silencing all sounds. The next day 177 and 143 stayed on spot until relieved by Div. 2, which stayed in the vicinity for two days. The morning of May 31, USS AYLWIN coming up laid a bomb barrage on a large oil patch nearby. Position was buoyed, but tide carried buoy under. Depth 40 fathoms. No evidence, except oil.