- Keegan, John
- Naval Intelligence, WWII operations, History - WW2
- RAN Ships
- None noted.
- March 2007 edition of the Naval Historical Review (all rights reserved)
Editor’s Note: In 2006, the Review published an article tracing the history of HMAS Rushcutter during the period 1939-45, when that establishment was the primary A/S training school throughout the Empire for both officers and sailors. Many Rushcutter graduates went on to serve throughout the Battle of the Atlantic. Their activities and achievements were recalled in a second article which accompanied the first. This article summarizes a detailed and thoroughly documented review of that Battle from an Intelligence point of view, and provides some very revealing statistics.
Taken from Intelligence in War by John Keegan, published by Hutchinson of London, 2003. Reprinted here with the kind permission of the publishers, Random House, of London.
The Allies – the British and Canadians first, the Americans later – enjoyed superior tactical intelligence throughout the Atlantic battle. They had sonar (Asdic) from the start, HF/DF and centimetric radar from 1942, aerial surveillance – of expanding range – from 1939. There were serious lapses, associated with shortages of escorts in 1939‑41 and with American refusal to form convoys in the first six months of 1942. Nevertheless, while tactical intelligence collected by the U-boats was limited by a patrol line’s line of vision, supplemented eventually and only close to France by that of the Condor aircraft, the convoy escorts and their associated patrol aircraft always had the edge, which increased throughout the war. Eventually the Allies’ tactical advantage became overwhelming.
The question of the importance of intelligence in the Atlantic battle therefore turns on the strategic issue: B-dienst versus Bletchley. The B-dienst was a remarkable organisation. Working largely with human resources, rather than the electro-mechanical devices later available in England and the United States, the German decoders – their target was the Naval Cypher No. 3, a book code mathematically super-encrypted – achieved impressive success for several long periods. Having broken the old (Royal) Naval Code, the system of five-digit groups, as early as 1935, it used the clues the Code provided to attack the newer Naval Cypher and by April 1940 were reading as much as 30 per cent of British transmissions. However the Naval Cypher and Code were replaced in August 1940 by new versions of each, against which the B-dienst had less success. It recovered its form when Naval Cypher No. 3 was introduced in June 1941 for transatlantic communication, and read it throughout 1942; in December it was reading 80 per cent of messages sent. Between 15 December, when the British added precautions, and February 1943, it was again in the dark but then found a way back, sometimes reading directives to convoys ten and twenty hours before the movements they ordered took place. Not until June, when an entirely new cipher was distributed, were British signals at last made secure.
Bletchley Park, Enigma & Tiger
On their side, the British, and later the Americans of OP-20-G in Washington, experienced similar periods of light and dark. The British benefited from a series of captures during 1940 and 1941 – of U-33 in February 1940, of the patrol boat VP2623 in April and, in March 1941, of the trawler Krebs during the commando raid on the Norwegian Lofoten Islands. In May and June the weather ships Munchen and Larenburg were seized in deliberate ‘cutting out’ operations, while on 9 May U-110 fell into British hands. Each yielded some material – either parts of the Enigma machine, or gridded charts, or enciphering material – which, when added to what Bletchley had been able to reconstruct from interceptions, furthered decryption. Traffic for February, May, June and July 1941 was read in part or whole as a result, and some in real time. After August 1941 until February 1942, the Heimisch key, called Dolphin at Bletchley, was read at a delay of not more than thirty-six hours. The decryption was considerably assisted by the deployment of the first bombes, which greatly assisted in the identification of possible Enigma key settings. Much help was also provided by the carelessness of German operators in retransmitting Enigma messages previously enciphered in the dockyard (Werft) or weather ciphers, which were quite easily read.
After February 1942, however, Bletchley lost its way into the U-boat traffic, because of the German adoption of a new Enigma key, called Shark by the British, Triton by the Germans, on the first of the month. Regular reading in real time did not resume again until December 1942. This period coincided with the reciprocal B-dienst success against British naval ciphers and with a peak of German advantage in the Battle of the Atlantic. In June (129), July (136) and August (117), monthly sinkings exceeded one hundred ships. Total sinkings exceeded four million tons.