Editing Ultra (cryptography) (section)

===Effect on the duration of the War===
There has been controversy about the influence of Allied Enigma decryption on the course of World War II with three views – that without Ultra the outcome of the war would be different, that without Ultra the Allies would have still won but that it was shortened by two years and that while useful Ultra decrypts were largely incidental to the fact and timing of the Allied victory.

An oft-repeated assessment is that decryption of German ciphers advanced the [[Victory in Europe Day|end of the European war]] by no less than two years.{{sfn|Kahn|1997|p=}}<ref name="engima_cryptographic_mathematics">{{cite book |last=Miller |first=A. Ray |year=2001 |title=The Cryptographic Mathematics of Enigma |publisher=National Security Agency |url=http://www.nsa.gov/about/_files/cryptologic_heritage/publications/wwii/engima_cryptographic_mathematics.pdf |url-status=dead |archive-url=https://web.archive.org/web/20090117030740/http://www.nsa.gov/about/_files/cryptologic_heritage/publications/wwii/engima_cryptographic_mathematics.pdf |archive-date=17 January 2009 |access-date=14 January 2015 }}</ref> Hinsley, who first made this claim, is typically cited as an authority for the two-year estimate.<ref>{{cite web |last1=Hinsley |first1=F.H. |title=The Influence of ULTRA in the Second World War |url=http://www.cix.co.uk/~klockstone/hinsley.htm |website=Keith Lockstone's home page |access-date=13 May 2020}}</ref>

Winterbotham's quoting of Eisenhower's "decisive" verdict is part of a letter sent by Eisenhower to Menzies after the conclusion of the European war and later found among his papers at the Eisenhower Presidential Library.{{sfn|Winterbotham|1974|p=2}} It allows a contemporary, documentary view of a leader on Ultra's importance:

{{Quote|July 1945

Dear General Menzies:

I had hoped to be able to pay a visit to Bletchley Park in order to thank you, Sir Edward Travis, and the members of the staff personally for the magnificent service which has been rendered to the Allied cause.

I am very well aware of the immense amount of work and effort which has been involved in the production of the material with which you supplied us. I fully realize also the numerous setbacks and difficulties with which you have had to contend and how you have always, by your supreme efforts, overcome them.

The intelligence which has emanated from you before and during this campaign has been of priceless value to me. It has simplified my task as a commander enormously. It has saved thousands of British and American lives and, in no small way, contributed to the speed with which the enemy was routed and eventually forced to surrender.

I should be very grateful, therefore, if you would express to each and every one of those engaged in this work from me personally my heartfelt admiration and sincere thanks for their very decisive contribution to the Allied war effort.

Sincerely,

Dwight D. Eisenhower}}

There is wide disagreement about the importance of codebreaking in winning the crucial [[Battle of the Atlantic]]. To cite just one example, the historian Max Hastings states that "In 1941 alone, Ultra saved between 1.5 and two million tons of Allied ships from destruction." This would represent a 40 percent to 53 percent reduction, though it is not clear how this extrapolation was made.<ref>{{cite book|last1=Hastings|first1=Max|title=All Hell Let Loose: The World at War, 1939–45 |date=2011 |publisher=HarperPress |location=London|pages=275–276}}</ref>

Another view is from a history based on the German naval archives written after the war for the British Admiralty by a former U-boat commander and son-in-law of his commander, Grand Admiral [[Karl Dönitz]]. His book reports that several times during the war they undertook detailed investigations to see whether their operations were being compromised by broken Enigma ciphers. These investigations were spurred because the Germans had broken the British naval code and found the information useful. Their investigations were negative, and the conclusion was that their defeat "was due firstly to outstanding developments in enemy radar..."<ref>{{cite book|last1=Hessler|first1=Günther|title=The U-Boat war in the Atlantic, 1939–1945|date=1989|publisher=Her Majesty's Stationery Office|location=London}}'''2''', p. 26.</ref> The great advance was [[centimetric radar]], developed in a joint British-American venture, which became operational in the spring of 1943. Earlier radar was unable to distinguish U-boat [[conning tower]]s from the surface of the sea, so it could not even locate U-boats attacking convoys on the surface on moonless nights; thus the surfaced U-boats were almost invisible, while having the additional advantage of being swifter than their prey. The new higher-frequency radar could spot conning towers, and [[periscope]]s could even be detected from airplanes. Some idea of the relative effect of cipher-breaking and radar improvement can be obtained from [[Battle of the Atlantic|graphs]] showing the tonnage of merchantmen sunk and the number of U-boats sunk in each month of the Battle of the Atlantic. The graphs cannot be interpreted unambiguously, because it is challenging to factor in many variables such as improvements in cipher-breaking and the numerous other advances in equipment and techniques used to combat U-boats. Nonetheless, the data seem to favor the view of the former U-boat commander{{snd}}that radar was crucial.

While Ultra certainly affected the course of the [[Western Front (World War II)|Western Front]] during the war, two factors often argued against Ultra having shortened the overall war by a measure of years are the relatively small role it played in the [[Eastern Front (World War II)|Eastern Front conflict between Germany and the Soviet Union]], and the completely independent development of the U.S.-led [[Manhattan Project]] to create the [[atomic bomb]].  Author [[Jeffrey T. Richelson]] mentions Hinsley's estimate of at least two years, and concludes that "It might be more accurate to say that Ultra helped shorten the war by three months – the interval between the actual end of the war in Europe and the time the United States would have been able to drop an atomic bomb on Hamburg or Berlin – and might have shortened the war by as much as two years had the U.S. atomic bomb program been unsuccessful."<ref name="richelson"/>  Military historian [[Guy Hartcup]] analyzes aspects of the question but then simply says, "It is impossible to calculate in terms of months or years how much Ultra shortened the war."<ref name="hartcup">{{cite book | first=Guy | last=Hartcup | author-link=Guy Hartcup | title=The Effect of Science on the Second World War | publisher=Macmillan Press | location=Basingstoke, Hampshire | date=2000 | pages=96–99}}</ref>

[[F. W. Winterbotham]], the first author to outline the influence of Enigma decryption on the course of World War II, likewise made the earliest contribution to an appreciation of Ultra's ''postwar'' influence, which now continues into the 21st century{{snd}}and not only in the postwar establishment of Britain's [[GCHQ]] (Government Communication Headquarters) and the United States' NSA. "Let no one be fooled", Winterbotham admonishes in chapter 3, "by the spate of television films and propaganda which has made the war seem like some great triumphant epic. It was, in fact, a very narrow shave, and the reader may like to ponder [...] whether [...] we might have won [without] Ultra."{{sfn|Winterbotham|1974|p=25}}

Iain Standen, Chief Executive of the Bletchley Park Trust, says of the work done there:  "It was crucial to the survival of Britain, and indeed of the West."  The Departmental Historian at [[GCHQ]] (the Government Communications Headquarters), who identifies himself only as "Tony" but seems to speak authoritatively, says that Ultra was a "major force multiplier. It was the first time that quantities of real-time intelligence became available to the British military."{{cn|date=May 2025}}

According to the official historian of [[British Intelligence]], Ultra intelligence shortened the war by two to four years, and without it the outcome of the war would have been uncertain.{{sfn|Hinsley|1996}}