Ultra was the high-grade intelligence made available to Allied forces throughout WW II, thanks to the UK's breaking of the Wehrmacht's Enigma ciphers. Bennett, one of the Oxbridge dons employed at Bletchley Park to intercept and decode Nazi Germany's wireless messages, provides fresh perspectives on the role Ultra played in the European theater from 1941 through 1944. Author of Ultra in the West (1980), which focused on the last 18 months of the war (including preparations for D-day), he would have preferred to write in chronological order; the vagaries of declassification schedules made this impossible, however. Bennett provides new slants on the importance of Ultra in cutting Rommel's North African supply lines and its contributions to Montgomery's triumph at Alamein. Also covered are the invasions of Sicily and Italy as well as the battle for Crete (which the author judges an Allied victory in that it helped prevent an occupation of Malta). In addition, Bennett offers revelatory information on how Tito's Partisans were able to seize control of Yugoslavia for the communist cause. The principal advantage of Ultra over other sources of military/diplomatic intelligence was its absolute reliability. Almost equally valuable, in Bennett's view, were the order-of-battle insights decrypts afforded Allied commanders. Absent personal appraisals, he concedes, there's really no telling the weight accorded Ultra signals in their strategic (and tactical) decisions. On the basis of outcomes at crucial stages of campaigns in and around the Mediterranean, though, Bennett concludes that Ultra's influence was at least significant. A first-rate interpretive briefing on the use (and, occasionally, disuse) of Ultra intelligence in thwarting Axis operations and ambitions at a time when Hitler's Reich was still riding high.