When leaving Alexandria on 18 May: British destroyers HMS Eridge (L 68) (LtCdr W.F.N. Gregory-Smith, DSC, RN) and HMS Hero (H 99) (Lt W. Scott, RN), corvettes HMS Delphinium (K 77) (Cdr R.L. Spalding, RN) and HMS Snapdragon (K 10) (T/Lt P.H. Potter, RNVR) and armed whalers HMS Cocker (T/Lt J. Scott, RNVR) and HMS Falk (FY 789) (Lt J.G. Jones, RNR)
British destroyers HMS Dulverton (L 63) (LtCdr W.N. Petch, OBE, RN) and HMS Hurworth (L 28) (LtCdr J.T.B. Birch, RN) acted as striking force

* U-boats that fired torpedo or used the deck gun

In the afternoon of 18 May, 1942, the convoy AT-46 left Alexandria consisting of five merchant ships, escorted by four destroyers that formed an outer ring and two corvettes and two armed whalers as close screen. The convoy proceeded in three columns, but owing to heavy seas and a strong headwind at only 4 to 5 knots. The poor speed upset the carefully arranged routing and brought the convoy to positions where there was the greatest danger from U-boats during dark hours instead of daylight.

At 19.11 hours on 20 May, U-431 spotted the ships about 65 miles east of Tobruk, submerged immediately, passed close to the leading escorts and dived deep after firing two torpedoes at the biggest of the five ships from within the convoy at 20.19 hours. One of the torpedoes struck the Eocene, the leading ship of the port column, which was immediately abandoned by her crew. The escorts initially believed that the attack came from the port side, fired star shells outwards from convoy and HMS Delphinium, HMS Hero and HMS Falk dropped depth charges over the suspected position of the U-boat, while HMS Snapdragon and HMS Hurworth did the same on the starboard side of the convoy. The Germans counted 21 depth charge explosions but none were close because U-431 remained undetected and managed to escape after surfacing at 23.45 hours. In the meantime HMS Cocker picked up the survivors and stood by the abandoned tanker, screened by HMS Falk and HMS Snapdragon with HMS Eridge and HMS Hurworth continuing the search for the attacker while the remaining escorts returned to the ships of the convoy. At 23.45 hours, the Eocene sank and soon all warships rejoined the convoy as no trace of the U-boat was found and escorted the other four ships to Tobruk, arriving on the morning of 21 May.