During World War II, Germany used two distinct categories of machine to encrypt messages prior to radio transmission. The first, Enigma, resembled a typewriter and was in very widespread use. The second, the so-called FISH machines, resembled teleprinters and were used only for the highest grade communications, usually between Berlin and the headquarters of various Army Groups.
German cryptanalysts were confident that both Enigma and FISH were unbreakable. They were profoundly mistaken. Throughout the war, British cryptanalysts regularly broke Enigma and FISH traffic at Bletchley Park in Buckinghamshire, and in doing so obtained vital information, called ULTRA, which changed the course of history.
Enigma and the Contribution of the Bombes
Enigma traffic was initially broken by hand and later broken on an industrial scale using electro-mechanical machines called bombes, designed by Alan Turing and Gordon Welchman1.
Decrypted Enigma traffic played an important part in many of the critical battles of the war, including the evacuation from Dunkirk, the Battle of Britain, and the Battle of Alamein. ULTRA played a crucial and perhaps decisive role in the Battle of the Atlantic, the most vital battle of the war.
Although critical, these were all strategically defensive victories but the strategic ULTRA vital for the Normandy campaign was obtained primarily from the FISH traffic.
FISH and the Genesis of the Electronic Computer
FISH traffic was initially broken by hand, then later on a machine called 'Heath-Robinson' which consisted of about 30 valves and performed high-speed comparisons of two paper-tapes on which characters were represented by perforations. Heath-Robinson demonstrated the validity of the comparison method but was too slow and unreliable to be of operational value. What was required was a machine to perform electronically what 'Heath Robinson' did electro-mechanically.
Such a machine consisting of about 1600 valves was designed by Tommy Flowers2,3,4 and Colossus Mk. I, as it was named, was delivered to Bletchley Park in December 1943 and immediately proved successful. In March 1944, faced with a great increase in FISH traffic, Bletchley Park placed orders for twelve Colossus Mk. II each incorporating 2400 valves. The first Colossus Mk. II was delivered to Bletchley Park on the night of 31st May 1944, six days before D-Day, and was operational a few hours later.
The Contribution of Colossus to OVERLORD and the Normandy Campaign
No account primarily concerned with the content and operational significance of the decrypted FISH traffic has yet been published. This makes it difficult, even today, to assess the precise contribution Colossus made to ULTRA. What is known is that the FISH traffic contained the most vital secrets of the German High Command and that without Colossus the Allied penetration of the FISH ciphers could not have occurred in the abundance in which it did.
The first important FISH link broken by Colossus was that between Berlin and Kesselring, then Commander of German forces in Italy. ULTRA saved the Anzio beach-head in February 1944 by revealing the timing, direction, composition and scale of the German counter-offensive. By retaining the beach-head the Allies tied down substantial German forces which would otherwise have been available for the defence of France on D-Day.5
Unquestionably the most important contribution made by Colossus was its production of the FISH keys between Berlin and von Runstedt, Commander-in-Chief West, before OVERLORD and then, intermittently, throughout the Normandy campaign. ULTRA revealed the disposition of German forces, and particularly the panzer divisions, in the Normandy area many weeks before the invasion enabling the Allies to predict with considerable accuracy the German potential for counter-offensive operations. During 24-27th May 1944, ULTRA revealed that von Runstedt was moving two divisions to the area designated for US airborne landings, the Allies accordingly moved the dropping zone nearer to UTAH and OMAHA beaches.
On 4th June 1944, as Eisenhower and the other senior Allied commanders met to issue the orders to launch the invasion, they did so in the knowledge, provided by ULTRA, that the German High Command had no notion of where or when the blow would fall. Thus by revealing the innermost thoughts of the German High Command the dim glimmer of Colossus' thyratron rings silently supplied the Allied commanders with the confidence necessary to proceed with the greatest operation in military history.
In early August 1944, the link between Berlin and Army Group B was broken on Colossus, revealing that Hitler had personally ordered von Kluge to drive an armoured spearhead consisting of five panzer divisions with supporting infantry to Avranches to split the American forces in the Cherbourg peninsula.6 Foreknowledge of this offensive enabled the Allies to set a trap which resulted, two weeks later, in the annihilation of the German 7th Army at Falaise. It was the climax of the Normandy campaign and ULTRA had played a pivotal role. After the battle the German Army in France was everywhere in retreat. Hitler declared it to be the worst day of his life.
During the height of the Normandy campaign, Bletchley Park was deciphering a staggering 18,000 messages each day, and a cornucopia of reports from ULTRA continued to flow for the remainder of the war. Among the strategic situation reports broken by Colossus there were indications of severe fuel and aircraft shortages. Allied bombing policy was altered to exploit these weaknesses but the war, with the German Army routed from France, was already effectively won.
In May 1945 one message, when decrypted, read:
thus bringing the news that the war in Europe was finally at an end.
The Effect of ULTRA on History
ULTRA did not win the war. The entry of the United States, with its great wealth of materiel, and its capacity to produce the first atomic weapons made an allied victory ultimately inevitable, but in the early stages of the war ULTRA played a crucial role by helping Great Britain avoid defeat. If Britain had been defeated it is unlikely that the Soviet Union would have survived. Thus the United States, the sole free major industrial power would have been confronted by Europe under Nazi domination from Iceland to the Urals, and by Japan.
Although by the time Colossus became operational there was no realistic possibility of the Allies losing the war, Colossus nevertheless holds a place in history for the part it played in the success of OVERLORD and the Normandy campaign.
If OVERLORD had failed, there would have been no further opportunity for a second attempted invasion in 1944, and probably no enthusiasm for a second such attempt at all. Germany would have been able to rush reinforcements from the West to Eastern Europe which may have resulted in a reversal on the Eastern front.
In late 1944 and early 1945 German science was producing new and technologically advanced weapons. An Allied failure to break into Western Europe would have allowed Germany time to bring these weapons into operation in ever-increasing numbers. For example, the Messerschmitt 262 jet fighter was superior to anything the Allies had at that time. Equipped with this aircraft in quantity, the Luftwaffe could have wrested air superiority from the Allies rendering a second invasion attempt impossible and possibly halting the bomber offensive. It is unlikely that the Allies could have reversed this situation before late 1946.
Faced with such a scenario, and consistent with the Anglo-American 'Germany first' strategy, it is likely that after consultation with Britain, the United States would have selected perhaps Essen and Nuremberg, not Hiroshima and Nagasaki, as the targets for the first atomic bombs. Having witnessed the effects of the first atomic bombs on Germany it is likely that Japan would have surrendered unconditionally to avoid a similar fate.
Two weeks after Germany surrendered Allied intelligence learned of German penetration of high-grade Soviet ciphers - the Soviet equivalent of FISH. A number of German analysts and 7½ tons of their deciphering machines were taken to a location in England about 20 miles from Bletchley.7 It seems possible that with Soviet motives coming increasingly under scrutiny in the Cold War, the Colossi remained in employment
When Britain revealed the existence of ULTRA to the United States in 1941, a rapport developed between the intelligence communities of the two countries which persisted throughout the war, the cold war which followed8 and which continues to this day.
(1) W. G. Welchman. The Hut Six Story.
Allen Lane. 1982.
(2) T. H. Flowers. The Design of Colossus. Annals of the History of Computing, 5 (1983), 239-52.
(3) A. W. M. Coombs. The Making of Colossus. Annals of the History of Computing, 5 (1983), 253-59.
(4) W. W. Chandler. The Installation and Maintenance of Colossus. Annals of the History of Computing, 5 (1983), 260-262.
(5) Ed. Hinsley & Stripp. Codebreakers. The Inside Story of Bletchley Park. Oxford Univ. Press. 1993.
(6) Ralph Bennett. ULTRA in the West. The Normandy Campaign of 1944-45. Hutchinson. 1979.
(7) Thomas Parrish. The ULTRA Americans. pp 282-284. Stein and Day. 1986.
(8) Bradley F Smith. The ULTRA-Magic Deals and the Most Secret Special Relationship. Airlife. 1993.
Copyright © Graham Ellsbury 1997
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