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The U-boat attack on Convoy HX239 was the last big convoy battle of May 1943, and marked the effective defeat of the U-boats in the North Atlantic. As often happened in 1943 the German code-breakers at B-Dienst had discovered the location and course of the convoy, allowing Dönitz to set up an ambush. The code-breakers at Bletchley Park had discovered the ambush and the convoy had been diverted, but the orders changing to change course had been intercepted, and themselves decoded, allowing the Germans to move their ambush.
By mid-May the Germans had suffered a series of defeated in convoy battles, and on 21 May U-boat command recognised this in their pre-battle signal to the U-boats - “If there is anyone who thinks that combating convoys is no longer possible, he is a weakling and no true U-boat captain. The battle of the Atlantic is getting harder but it is the determining element in the waging of the war”. This message was also intercepted and decoded at Bletchley Park.
The attack began on 22 May, but despite the large number of U-boats involved not a single merchant ship was lost. Two escort carriers – USS Bogue and HMS Archer – were protecting the convoy. Aircraft from USS Bogue sank U-569, while the Archer sank U-752. When taken alongside the defeat of the attack on Convoy SC130 and earlier defeats against HX237 and SC129 in mid-May and ONS5 at the start of May, the failure of these large scale German attacks on convoys marked the defeat of Dönitz’s wolf packs in the North Atlantic.