Advances in technology and warfare

During the war, aircraft continued their roles of reconnaissance, fighters, bombers and ground-support from World War I, though each area was advanced considerably. Two important additional roles for aircraft were those of the airlift, the capability to quickly move high-priority supplies, equipment and personnel, albeit in limited quantities;[251] and of strategic bombing, the targeted use of bombs against civilian areas in the hopes of hampering enemy industry and morale.[252] Anti-aircraft weaponry also continued to advance, including key defences such as radar and greatly improved anti-aircraft artillery, such as the German 88 mm gun. Jet aircraft saw their first limited operational use during World War II, and though their late introduction and limited numbers meant that they had no real impact during the war itself, the few which saw active service pioneered a mass-shift to their usage following the war.[253]

At sea, while advances were made in almost all aspects of naval warfare, the two primary areas of development were focused around aircraft carriers and submarines. Although at the start of the war aeronautical warfare had relatively little success,[254] actions at Taranto, Pearl Harbor, the South China Sea and the Coral Sea soon established the carrier as the dominant capital ship in place of the battleship.[255][256] In the Atlantic, escort carriers proved to be a vital part of Allied convoys, increasing the effective protection radius dramatically and helping to seal the Mid-Atlantic gap.[257] Beyond their increased effectiveness, carriers were also more economical than battleships due to the relatively low cost of aircraft[258] and their not requiring to be as heavily armoured.[259] Submarines, which had proved to be an effective weapon during the first World War[260] were anticipated by all sides to be important in the second. The British focused development on anti-submarine weaponry and tactics, such as sonar and convoys, while Germany focused on improving its offensive capability, with designs such as the Type VII submarine and Wolf pack tactics.[261] Gradually, continually improving Allied technologies such as the Leigh light, hedgehog, squid, and homing torpedoes proved victorious.

Land warfare changed drastically from the static front lines predominating in World War I to become much more fluid and mobile. An important change was the concept of combined arms warfare, wherein tight coordination was sought between the various elements of military forces; the tank, which had been used predominantly for infantry support in the First World War, had evolved into the primary weapon of these forces during the second.[262] In the late 1930s, tank design was considerably more advanced in all areas then it had been during World War I,[263] and advances continued throughout the war in increasing speed, armour and firepower. At the start of the war, most armies considered the tank to be the best weapon against itself, and developed special-purpose tanks to that effect.[264] This line of thinking was all but negated by the poor performance of the relatively light early tank armaments against armour, and German doctrine of avoiding tank-versus-tank combat; the latter factor, along with Germany's use of combined arms, were among the key elements of their highly successful blitzkrieg tactics across Poland and France.[262] Many means of destroying tanks, including indirect artillery, anti-tank guns (both towed and self-propelled), mines, short-ranged infantry antitank weapons, and other tanks were utilized.[264] Even with large-scale mechanization of the various armies, the infantry remained the backbone of all forces,[265] and throughout the war, most infantry equipment was similar to that utilized in World War I.[266] However the United States became the first country to arm its soldiers with a semi-automatic rifle, in this case the M-1 Garand. Some of the primary advances though, were the widespread incorporation of portable machine guns, a notable example being the German MG42, and various submachine guns which were well suited to close-quarters combat in urban and jungle settings.[266] The assault rifle, a late war development which incorporated many of the best features of the rifle and submachine gun, became the standard postwar infantry weapon for nearly all armed forces.

In terms of communications, most of the major belligerents attempted to solve the problems of complexity and security presented by utilizing large codebooks for cryptography with the creation of various ciphering machines, the most well known being the German Enigma machine.[267] SIGINT (signals intelligence) was the countering process of decryption, with the notable examples being the British ULTRA and the Allied breaking of Japanese naval codes. Another important aspect of military intelligence was the use of deception operations, which the Allies successfully used on several occasions to great effect, such as operations Mincemeat and Bodyguard, which diverted German attention and forces away from the Allied invasions of Sicily and Normandy respectively.

Other important technological and engineering feats achieved during, or as a result of, the war include the worlds first programmable computers (Z3, Colossus, and ENIAC), guided missiles and modern rockets, the Manhattan Project's development of nuclear weapons, the development of artificial harbours and oil pipelines under the English Channel.