Kahn, David. "Enigma Uncracked"
What if: Many German military transmissions, especially those of the navy, went undecoded by the Allies.
Summary: Essay which speculates that Rommel would have captured Cairo, his fuel supplies having not been sunk, but would been unsuccessful in linking up with other German forces in the Russian oil fields. In the Atlantic, submarine warfare would likely have prevented a buildup of troops in Britain, and in the end nuclear weapons would have been necessary to defeat Nazi Germany.
Published: In What If? 2: Eminent Historians Imagine What Might Have Been (ed. Robert Cowley), q.v.