The war brought new methods for future wars. The air forces improved greatly in fields such as air transport, strategic bombing (to use bombs to destroy industry and morale), as well as radar, and weapons for destroying aircraft. Jet aircraft were developed and would be used in worldwide air forces.
At sea, the war focused on using aircraft carriers and submarines. Aircraft carriers soon replaced battleships. The important reason was they were cheaper. Submarines, a deadly weapon since World War I, also played an important part in the war. The British improved weapons for destroying submarines, such as sonar, while the Germans improved submarine tactics.
The style of war on the land changed from World War I to be more moveable. Tanks, which were used to support infantry, changed to a primary weapon. The tank was improved in speed, armour and firepower during the war. At the start of the war, most commanders thought that using better tanks was the best way to fight enemy tanks. However, early tanks could harm armour just a little. The German idea to avoid letting tanks fight one another meant tanks facing tanks rarely happened. This was a successful tactic used in Poland and France. Ways to destroy tanks also improved. Even though vehicles became more used in the war, infantry remained the main part of the army, and most equipped like in World War I.
Submachine guns became widely used. They were especially used in cities and jungles. The assault rifle, a German development combining features of the rifle and submachine gun, became the main weapon for most armies after the war.
Other developments included better encryption for secret messages, such as the German Enigma. Another feature of military intelligence was the use of deception, especially by the Allies. Others include the first programmable computers, modern missiles and rockets, and the atomic bombs.