The U-boat attack on convoy HX237 of 7-14 May 1943 was the second of a series of defeats inflicted on Dönitz’s U-boats that forced the wolf-packs to withdraw from the North Atlantic. Throughout May both the British and German code-breakers were reading each others messages, and at this point the advantage in the cryptographic war was with the Germans. Their code-breakers discovered the route of Convoy HX237. British code-breakers discovered this, and the convoy was re-routed. In some cases this ended the battle, but on a number of occasions the German code-breakers read the messages moving the convoy, and the ambush was moved.
The convoy was protected by the 5th Escort Group, which contained the escort carrier HMS Biter, and was covered by shore-based VLR Liberators. As many as thirty six U-boats attacked the convoy between 7-14 May 1943, but in a sign of the falling morale and determination of U-boat commanders only three merchantmen were attacked. During the course of the attack the long range aircraft sank one U-boat, and helped the surface ships sink a second, while the aircraft from HMS Biter sank a third U-boat for the loss of one aircraft. The 5th Escort Group them moved on the protect convoy SC129, and in the attack on this convoy the Germans would again lose one U-boat for each ship they sank.