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Some considerable time ago I found, spread over a number of files, a very brief account of the active/passive maneuvers in the signals intelligence war from very late 1942 to very late 1943 covering operations in the North Atlantic. It was a little frustrating in that it raised more questions than answered.
The first recorded instance of intercepted voice transmission by a U-boat occurred in some of the earliest CURRENT radio traffic. This was contained in intercepted signals sent by U 524 on 5/12/42 as part of Group Panzer. Then there was a gap with nothing collected until April 1943. In this instance, German intercepts were made in order to overcome foggy conditions and generally bad weather. These attempts were made to try and locate convoys SC 126 and/or HX 233. This failed because both convoys were re-routed away from the U boat group as a result of Ultra intercepts and D/Fing.
Although the late 1943 U-bost offensive in the North Atlantic failed, the threat posed by German radio intercept parties on certain U-boats was appreciated by the British and efforts were made to thwart further German efforts in this field. By early November 1943, CinC Western Approaches had promulgated proposals for AS escorts to be detached and to then transmit fake voice convoy signals, and in mid December attempts were made to implement this counter measure to confuse U boat Group Coronel.
In addition to fake traffic, the convoy itself was ordered to avoid transmitting radio signal as much as possible, and for escorts to be wary of being mislead by the Germans sending fake messages to escorts so that they might respond.
The Germans believed (falsely) that the failure to find the convoys in this particular offensive was due to the Allies using a very long range airborne radar which could locate the U-boats and allow a re-routing of convoys away from danger.
The radio intercept programme was generally abandoned in the Atlantic, but was retained in the Arctic where it continued to be used to a considerable degree.
Following the failure of the late 1943 offensive, the Germans immediately put into place the use of very long range reconnaissance aircraft (JU 290) for the location of the convoys and of the homing of U-boats onto them. This also failed.
It should be noted that although the Germans could DF on the MF voice traffic they could not on any of the HF signals. As for VHF voice signals, no U-boat was fitted with intercept equipment until around December 1943, and there was no VHF DF gear.
If this short account has been published already, I apologize.
Comments welcome.