Attack Aircraft
The United States relied on repurposed fighter aircraft such as the P-47 and the P-51 (in its special attack variant, designated as the A-36 Apache) to carry out attack missions. Light bomber aircraft included the Douglas A-20 Havoc, about 7,500 of which were constructed during the war. Douglas later developed the A-26 Marauder, a light bomber that entered service in 1943 and continued to serve through the Vietnam War.
Medium Bombers
Martin's B-10 bomber design, with its all-metal construction, was revolutionary when it first flew in 1932, but rapid advances during the 1930s rendered it obsolete by the dawn of American involvement in World War II. The B-18 Bolo, derived from Douglas' DC-2 transport aircraft, was deployed as the United States entered the war but was quickly retired from service. The Army Air Force's medium bomber fleet primarily was composed of the Martin B-26 Marauder and the North American B-25 Mitchell -- the latter most famous, perhaps, for its role in the "Doolittle Raid" on Tokyo in April 1942.
Strategic Bombers
The icon of American air power during World War II, of course, is based on the Bomber Command and its massive fleets of heavy bombers. Three aircraft made up the backbone of America's heavy bomber force. The Consolidated B-24 Liberator, the most-produced American military aircraft of all time, is nonetheless the least famous of the three. More well-known are the B-17 Flying Fortress, immortalized in movies such as 1990's "Memphis Belle," and the Boeing B-29 Superfortress, used to perform the only atomic bombing in history.
Torpedo Bombers
The widespread use of naval forces over great distances during World War II also necessitated the use of torpedo bomber aircraft as an effective counter. Torpedo aircraft employed by the United States included the Douglas TBD Devastator and the Grumman TBF Avenger (also produced by Martin under license as the TBM). The TBF entered popular culture as the aircraft that composed "Flight 19," the group of aircraft whose disappearance in 1945 helped fuel the mystery of the so-called Bermuda Triangle.