One of the most fascinating things about WWII is the extent to which the English were able to obtain secret information about the Axis and the incredibly skill with which they broke the codes and ciphers of the Enigma machine. While much of the credit goes to the carelessness of the Axis in transmitting the information, people were unaware of what they were doing at Bletchley Park until the 1970s, when the classified nature of the entire operation was lifted.
Ultra was the codename used by the British authorities in the Second World War for intelligence obtained from the more important enemy cyphers. From the spring of 1941 they broke these cyphers to an unprecedented extent and with little delay. Their success has two explanations.
The extent to which Ultra’s assistance brought forward this allied victory against the U-boats and made it so decisive is conjectural. But it is unlikely that, without the benefit of Ultra from the beginning of 1943, the Allies would have prevailed in the rate of shipbuilding and the destruction of U-boats in time to launch Overlord in the summer of 1944. it may be that by stripping resources from the Pacific, and on the assumption that they were not operating in the Mediterranean, they could have assembled enough troops and landing-craft in the United Kingdom to attempt a cross-channel invasion by the spring of 1945. But even if the U-boats had delayed matters only by those few months, the consequences for the success of Overlord would have been serious. And the consequences of a continuing lack of Ultra while Overlord was being prepared would have been no less grave.
Carried out when it was, in 1944, Overlord was planned around the fact that the Allies knew from Ultra – and thus knew for certain – the number and whereabouts of most of the German Army’s armoured divisions and other mobile formations, and could thus calculate the rate at which the enemy could build up counter-attacks and the directions from which they must come. With this intelligence they could risk making this first sea-borne invasion against Panzer opposition within a very narrow margin of ground superiority during the assault phase. Without Ultra they would have had to widen this margin or carry out considerable diversionary operations.
Even if they had been able to assemble the necessary extra troops and landing-craft by 1945, other problems would then have imposed further delay. By the spring of 1945 Germany would have completed the massive coastal defences of the Atlantic wall. Her V-weapon offensives against the United Kingdom would have been in full swing. She was bringing jet and rocket aircraft into service, and was about to deploy the revolutionary new U-boats against the sea-lanes. In the absence of a Mediterranean campaign she would not have had to disperse her forces to maintain the large army which in 1944 she kept in Italy. It is not unreasonable to assume that, in so difficult a situation, Overlord would have had to be deferred beyond 1945 and that, even if it had been possible to carry it out in 1946, it would have been a more onerous and prolonged undertaking than it proved to be in 1944.
In these circumstances the Allies would not have been inactive in other directions, but what different strategies would they have pursued? Would Soviet Russia have meanwhile defeated Germany or vice versa, or would there have been stalemate on the eastern fronts? What would the Allies have decided about the atom bomb, which Germany had not developed? Such questions are beyond the proper reach of counter-factual analysis, but fortunately they are questions that do not arise because the war went as it did. On the other hand, historians, who are concerned with the war as it was, must still ask why it went as it did. And they need venture only a reasonable distance beyond the facts to recognise the extent to which the explanation lies in the influence of Ultra.
I found a great article on one of the people that worked at Bletchley Park, Enigma code breaker Mavis Batey, over at No More Sad Computer. I thought it was incredible that she was unable to talk about her work to even her children. Thankfully she was married to someone that worked there as well during the war, otherwise she would have gone insane.