The American escort group A3 (Cdr Heineman) consisting of the cutter Spencer, the destroyer Greer, the British corvettes Dauphin and Dianthus and the Canadian corvettes Rosthern and Trillium. In the convoy is also the rescue ship Melrose Abbey.

The Wolfpack Westmark of 17 boats:
U-228 (Kptlt. Christophersen), U-230 (Kptlt. Siegmann) *, U-332 (Oblt. Hüttemann), U-359 (Oblt. Förster), U-405 (Korvkpt. Hopmann) *, U-409 (Oblt. Massmann) *, U-432 (Kptlt. Eckhardt), U-448 (Oblt. Dauter), U-523 (Kptlt. Pietzsch), U-526 (Kptlt. Möglich) *, U-527 (Kptlt. Uhlig) *, U-566 (Kptlt. Hornkohl), U-591 (Kptlt. Zetsche) *, U-616 (Oblt. Koitschka) *, U-634 (Oblt. Dalhaus), U-659 (Kptlt. Stock), U-709 (Oblt. Weber)

The Wolfpack Ostmark of 9 boats:
U-190 (Kptlt. Wintermeyer) *, U-229 (Oblt. Schetelig) *, U-439 (Oblt. Tippelskirch), U-447 (Kptlt. Bothe), U-530 (Kptlt. Lange) *, U-618 (Kptlt. Baberg), U-641 (Kptlt. Rendtel), U-642 (Kptlt. Brünning) *, U-665 (Oblt. Haupt)

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

The convoy initially avoids the patrol lines Burggraf and Wildfang but then runs into U-405. On the receiving of the sighting report, the BdU forms the patrol lines Ostmark (only from the 8th on) and Westmark.

The convoy has a lot of stragglers who have difficulties in keeping up with the convoy due to the bad weather. The escort group A3 is in bad shape also, taking up the escort of SC-121 only a few days after the disaster of ON-166. Most of the escort vessels have problems with their equipment and need urgent repairs or even dry-docking.

Still, when on the 6th the escort is aware of the build-up of an U-boat concentration, the commander sends out his fast escort vessels towards HF/DF contacts. Before dark a sharp course change is ordered in an attempt to shake off the boats but without result: U-566 and U-230 make contact and the latter sinks one ship in the night. This event goes unnoticed in the heavy gale and the rescue ship is not warned. One merchant ship recovers survivors but in doing so becomes a straggler himself and this ship is sunk towards morning by the U-591.

All day on the 7th U-228, U-230, U-409, U-591 and U-634 keep contact but the gale makes any successful attacks impossible. The next day the weather improves and the boats of the newly formed gruppe Ostmark make contact. In the morning U-527s attack but misses the convoy. In the evening U-190, U-527, U-591 and U-642 each sink a straggler.

No attacks are made in the night and on the 9th the escort is reinforced by the cutters Bibb and Ingham and the destroyer Babbitt. Also air escort is provided from Sqdn. 120. They manage to drive off the contact keeping U-566. Also U-230, U-332, U-405, U-409, U-641 and U-665 preparing for attack at night are repulsed. Only U-229 is able to attack but misses.

In the evening of the 9th U-530 sinks a straggler. U-405 and U-409 attack simultaneously at night and sink one and two ships respectively. U-229 makes another attack and sinks and damages one ship.

The next day the weather is deteriorating again. Only U-229, U-523, U-616, U-634 and U-642 are able to keep contact. Attacks from U-229 and U-616 fail and contact is lost. The escort is further reinforced by the British corvettes Campion and Mallow but the operation is broken off next day.

This battle was just one in a long series of big convoy battles in which the U-boats tried to disrupt the vital North Atlantic supply route to Britain. The convoy system seemed less and less useful as the wolfpacks decimated convoy after convoy. But encouraging for the British was the fact that a significant number of the ships were sunk outside the convoy, as rompers or stragglers without escort, thus proving the need of convoys.

In fact, escort groups were just too few, small and overworked to cope with the continually growing U-boat fleet. The number of escorts would have to increase significantly in order to revert this dangerous situation and it would take Churchill still another couple of convoy battles to realise just that.