Most Secret Source: The Role of Enigma in WWII

How did ULTRA shape the course of the war? At times, it played a major role in the turning of battle, at other times did not, at still others was fatally misused, and at still others was beneficial but not necessary to bring about victory in any case. Unfortunately, good intelligence is often badly used by its masters. ULTRA was no different. Did ULTRA win the war? No, men and tanks and bombs and airplanes did.
Did ULTRA shorten the war? Given the extent to it which it provided foreknowledge, once the balance of military forces was relatively close the answer must be yes. Did ULTRA prevent an earlier end to the war either by creating such confidence that avoidable mistakes were made in the rush for glory, or by preventing acceptance of an outcome short of unconditional surrender, or by causing the Allies to discount internal German opposition and a possible suicide attempt on Hitler? No, for its benefits outweighed its negative.
Does the glory of the victory become tainted in light of ULTRA? Yes, for not only does it reveal the extent to which our commanders knew in advance of German battle strengths and location, thus giving them a decided advantage, it also points out several egregious errors on their part despite possession of ULTRA. Can intelligence be counted on to provide us victory in future conflicts. No. ULTRA use and implementation was clearly deficient for two to three years, and came about only with the help of Polish and French contributions which we cannot count on in the future.
As Welchman points out, that may well mean suicide in a world where computers and ICBM's reduce the drag time to seconds from years. What role did ULTRA play? To quote one of the examiners: "Ultra was a war winner" even if not "the war winner."