The RAF rapidly realized the need for heavy bombers to replace the twin-engined Wellington and obsolete Hampden, and by 1943 three new four-engined bombers were in service: the underpowered, slow, Stirling, the workman-like Halifax, and the outstanding Lancaster. However, despite up-to-date aircraft, the technology of bombsights and navigation was sadly lacking, and the night attacks tended to drop bombs over wide areas of Germany's cities instead of precision targeting.

The USAAF, established in 1941, began a daylight precision bombing campaign from Great Britain against Germany with Boeing B-17 and Consolidated B-24 aircraft, equipped with the Norden predicting bombsight, in 1943. The American aircraft sacrificed bomb load in favour of heavy defensive armament-twelve 0.5-inch machine-guns aboard the B-17. However, despite their accurate name, the Flying Fortresses suffered appalling losses: over 8,000 of the 15,000 sent to Europe were shot down by enemy fire, and another 1,000 were destroyed in training accidents.

The appearance of long-range escort fighters like the Republic P-47, North American P-51, and Lockheed P-38 helped turn the tide of the great daylight air battles fought high over Germany in favour of the USAAF. At night, new electronic navigation aids, such as the beam-following Oboe and H2S radar-mapping, guided the RAF's bombers more accurately to their targets-where the precision-bombing Pathfinder force had laid flare markers to ensure that the huge numbers of bombs dropped from up to 1,000 aircraft did the most damage. During 1944 and early 1945, the USAAF struck Germany during the day, while the RAF attacked at night. One by one, Germany's cities were reduced to rubble.

Tactical air power also played a major role. Allied air forces, equipped with ever-improving versions of the Spitfire, the speedy P-51 Mustang, and new heavy fighters like the Hawker Typhoon and Tornado, had swept German aircraft from the skies over the Normandy beaches prior to the D-Day invasion of June 6, 1944. They would maintain battlefield air superiority for the remainder of the conflict. Bombers like the Martin B-26, and fighter aircraft doing double duty as ground attack machines, battered the German defenders in front of the advancing Allied armies.

In the Pacific, an entirely new kind of air war was being fought. Its reliance on carriers set the tone for naval warfare and aviation for the rest of the century. Japan opened the Pacific war with air attacks on Pearl Harbor, Hawaii, and other United States and British bases in the Pacific on December 7 and 8, 1941.