The Douglas A-26, the last aircraft designated as an "attack bomber" was designed to replace the Douglas A-20 Havoc/Boston. It incorporated many improvements over the earlier Douglas designs. The first three XA-26 prototypes first flew in July 1942, and each was configured differently: Number One as a daylight bomber with a glass nose, Number Two as a gun-laden night-fighter, and Number Three as a ground-attack platform, with a 75-millimeter cannon in the nose. This final variant, eventually called the A-26B, was chosen for production.
Upon its delivery to the 9th Air Force in Europe in November 1944 (and the Pacific Theater shortly thereafter), the A-26 became the fastest US bomber of WWII. The A-26C, with slightly-modified armament, was introduced in 1945. Following the war, the A-26 was updated and adapted as the needs of the new U.S. Air Force changed. It is the only combat aircraft to see active service in three conflicts: World War II, Korea, and Vietnam.