Military intelligence played a key role in the Allied victory of WWII. By 1943 the Allies had broken the key military and diplomatic codes for Germany and Japan and often had a better idea about the battle plans than the Axis generals. Strategic bombing also played a key role by hitting industries such as oil, electricity, and manufacturing that made mechanized war possible. The Allied use of the Norden bomb sight made strategic bombing easier, as bombers could now adjust for the speed of the plane and wind speed when dropping bombs. While the Germans did this as well with their Luftwaffe, the Allied use of air support in ground campaigns, especially after D-Day was essential. By late 1944 the Allies nearly had complete air superiority over the Germans in this war of attrition. In naval warfare, Allied forces brought back the convoy system which kept destroyers and cruisers close enough to attack German U-boats. The U-boats would continue to be a threat, however, until the concrete submarine pens were captured in France after D-Day.
In the Pacific Theater, Douglas MacArthur used an island-hopping campaign that captured key islands which were then converted to American air bases. This ultimately allowed American bombers to firebomb the main Japanese island of Honshu with as little loss of American lives as possible. American submarines preyed relentlessly on the Japanese merchant marine, and by summer 1945 Japanese civilians faced shortages and starvation. Of course, probably the greatest strategy was the use of two atomic bombs in quick succession to bring about the end of the war.