This I found from the "enigma" pages. As usual, no references.

From reading “ultra” material one gets the impression that, during the battle for Normandy in 1944 and the closing stages of the battle for the Atlantic in 1943, British and American Commanders knew almost every German move and order. The British passed on to the Russians the German plans and dispositions for the Battle of Kursk, which was decisive for the outcome of the war on the Eastern Front.

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