There are several:-
+ The breaking of both the German and Japanese codes is possibly one of the most significant factors:-
- in the Battle of the Atlantic it enabled U-Boats to be tracked down and destroyed and gave important insights into German intentions and order of battle which enabled meagre resources to be concentrated where they were needed.
- in the Pacific it enabled US forces to anticipate Japanese intentions such as at the pivotal Battle of Midway
+ The invention and development of RADAR
- This helped save Britain in 1940 in the Battle of Britain, which in turn prevented the German invasion and thus provided the springboard for the eventual liberation of Europe. If Britain had been invaded the decisive battles in Europe such as the Normandy Landings and the Battle of the Bulge would not have been possible.
- Radar enabled the Allies to develop the Radar Proximity Fuse which meant that anti-aircraft fire was much more effective. This and search radar is what protected the US Navy during the Pacific War - and without which they may well have been defeated in the Marianas, Leyte Gulf and Okinawa. Without the capture of Pacific Islands such as the Marianas even weapons such as the atomic bomb would have been useless as no aircraft would have had the range to reach Japan.
+ Perhaps the biggest mistake on the part of the Germans was their invasion of Russia and Hitler's refusal to attempt to capture Moscow until it was too late in the year. This led inevitably to the German's defeat at Stalingrad and later at Kursk. Germany's complete underestimation of the severity of the Russian winter and the manpower resources available to Russia made defeat all but inevitable from the outset.
+ The other major German mistake was their failure to recognise fully that Britain could only be defeated by starvation and isolation by way of defeating the convoys. The number of U-boats produced was simply too small to allow this at the time when shipping was at its most vulnerable - before the introduction of proper escort groups including Escort Carriers equipped with HFDF (direction finding equipment to detect U boats from their radio transmissions) and escort destroyers and corvettes armed with forward-throwing depth charge equipment such as Squid and Hedgehog. This is in stark contrast to the very effective anti-shipping campaign operated by US submarines against Japan (once difficulties with the Mk XIII torpedo had been overcome) and the total failure of Japan to protect her shipping which was vital to her very survival. If Britain had been isolated by U Boat blockade then the vast production resources of the USA would have been neutralised because it would have been impossible to bring it to bear on the point of battle - the European coastline and the Russian Front via the Arctic Convoys. Churchill himself described the Battle of the Atlantic as the one that gave him the most concern.
+ The biggest mistake on the part of the Japanese was to attack the US in the first place. Many have argued that Japanese defeat was all but inevitable from December 7 1941 given the huge disparity in industrial capacity and lack of readily available resources, particularly oil.
+ Air power played a significant role in all aspects of WWII and interestingly both the Germans and the Japanese followed mistaken paths in this respect:-
- they both failed to develop any significant strategic capability... their tactical use of aircraft was superb for winning battles against weakened or unprepared oponents but could not in themselves ensure strategic victory
- both Japan and Germany failed in the training of new aircrew. Both kept their frontline pilots in action until they were killed or injured whilst the Allies rested their crews between tours, these rest periods being frequently used to impart knowledge to trainee crews and permitted them to return to the frontline as experienced leaders. This provided a continual supply of well-trained and combat-ready crews whilst for both Germany and Japan the well trained crews that started the war had all but gone by the end with no like-for-like replacements.