When leaving Alexandria on 23 December: British destroyer HMS Avon Vale (L 06) (LtCdr Peter A.R. Withers, DSO, RN) and corvette HMS Peony (K 40) (Cdr Martyn B. Sherwood, DSO, RN)
As striking force from 23 to 26 December: British destroyers HMS Kipling (F 91) (Cdr Aubrey St. Clair-Ford, RN) and HMS Legion (G 74) (Cdr Richard F. Jessel, RN)

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

In the evening of 23 Dec, 1941, the convoy AT-6 left Alexandria consisting of three small freighters and the boom defence vessel HMS Burgonet (Z 33), escorted by three destroyers and one corvette. Owing to heavy seas and a strong headwind the convoy proceeded at only 3 to 4 knots and one of the freighters even had to turn back as she could not keep up with the others. At 16.30 hours on 25 December, HMS Peony shortly left the convoy to investigate a large patch of oil and wreckage about 30 miles east-northeast of Sidi Barrani, locating a Denton type raft and the body of a Chinese sailor in an Admiralty Pattern life-belt. Both discoveries indicate that they came across the position where HMS Salvia had been sunk with all hands by U-568 (Preuss) after she had picked up survivors from Shuntien.

At 13.50 hours on 26 December, the submerged U-559 heard the ships of convoy AT-6 about 40 miles east of Tobruk, went to periscope depth and subsequently attacked the leading ship with a single torpedo at 14.29 hours. The torpedo struck Warszawa at the stern and the immobilized ship had to be taken in tow by HMS Peony after the corvette and HMS Burgonet had taken off all troops and most of the crew, while HMS Avon Vale screened the rescue operation and the other two destroyers carried out an unsuccessful ASDIC sweep in search for the attacker. Assuming that the ship had been mined, the destroyers then escorted the slow tow convoy and ordered the remaining freighter to continue to Tobruk together with the boom defence vessel. The U-boat however waited until dusk, surfaced and left the area at high speed after sinking the damaged ship with a torpedo fired from the stern tube at 19.30 hours. The three destroyers immediately carried out an anti-submarine hunt, but failed to locate the attacker despite illuminating the area with many star shells during the night. HMS Peony rescued the remaining survivors from Warszawa and then proceeded at full speed with HMS Avon Vale to escort the remaining two ships of the convoy to Tobruk, arriving early in the morning on 27 December.