The Battle of the Atlantic and Signals Intelligence

Contains the weekly series U-boat Situation and the more intermittent bulletin U-boat Trends, written during World War II by Rear Admiral J.W. Clayton and Commander Rodger Winn.


These documents relate on a weekly and, in some cases, daily basis, exactly what the British knew concerning the activities of the German U-boats during the Battle of the Atlantic. Circulation was restricted at the Admiralty to the First Lord, the First Sea Lord and perhaps five or six others while at Western Approaches Command and RAF Coastal Command, only the commanders-in-chief and three staff officers at each headquarters were even aware of the existence of U-boat decryption intelligence.

U-Boat Situation was a weekly series showing the worldwide deployment of German U-boats and giving a general account of their activities and those of the Allied anti-U-boat forces. The U-Boat Trends bulletins, on the other hand, were issued on an irregular basis as the situation demanded and were designed to keep readers abreast of the latest technological developments and strategic and tactical trends.

The first U-Boat Situation appeared on 15 December 1941 and publication continued on a weekly basis from 5 January 1942 until the end of the war. U-Boat Trends began publication on 2 November 1942 with special supplements produced as and when events warranted. Initially Rear Admiral Clayton, who had been recalled from retirement before the outbreak of the war to become head of the Operational Intelligence Centre within the Naval Intelligence Division, was the author of both publications. However on 8 August 1943 Commander Winn, a peacetime barrister who had been made head of the Submarine Tracking Room in 1940, took over writing U-Boat Situations while Clayton continued with U-Boat Trends.

Taken together, U-Boat Situation and U-Boat Trends, which were based on decryption and other largely signals derived intelligence and were written by two men at the centre of the Allied intelligence effort against the U-boats, are pivotal to understanding how the Battle of the Atlantic was fought and its eventual outcome. They not only provide an 'insider's' history of the conflict, but also show with exceptional clarity what the Allies knew at any given time.

While it is difficult, because of the extreme secrecy surrounding U-boat decryption intelligence, to reconstruct Allied decision-making, it is incontrovertible that the communications intelligence represented by these two publications gave the Allies a huge advantage over the U-boats.