The Douglas TBD Devastator was a torpedo bomber of the United States Navy, ordered in 1934, first flying in 1935 and entering service in 1937. At that point, it was the most advanced aircraft flying for the USN and possibly for any navy in the world. However, the fast pace of aircraft development caught up with it, and by the time of the Japanese attack on Pearl Harbor the TBD was already outdated. It performed well in some early battles, but in the Battle of Midway the Devastators launched against the Japanese fleet were almost totally wiped out. The type was immediately withdrawn from front line service, replaced by the Grumman TBF Avenger. Ordered on 30 June 1934, and entered into a U.S. Navy competition for new bomber aircraft to operate from its aircraft carriers, the Douglas entry was one of the winners of the competition. Other aircraft ordered for production as a result of the competition included the Northrop BT-1 which would evolve into the SBD Dauntless, the Brewster SBA and the Vought SB2U Vindicator. The XTBD Devastator, which flew for the first time on 15 April 1935, marked a large number of "firsts" for the U.S. Navy. It was the first widely-used carrier-based monoplane as well as the first all-metal naval aircraft, the first with a totally-enclosed cockpit, the first with power-actuated (hydraulically) folding wings; it is fair to say that the TBD was revolutionary. A semi-retractable undercarriage was fitted, with the wheels designed to protrude 10 in (250 mm) below the wings to permit a "wheels-up" landing with only minimal damage. A crew of three was normally carried beneath a large "greenhouse" canopy almost half the length of the aircraft. The pilot sat up front; a rear gunner/radio operator took the rearmost seat, while the bombardier occupied the middle seat. During a bombing run, the bombardier lay prone, sliding into position under the pilot to sight through a window in the bottom of the fuselage, using the Norden Bombsight.