In 1967 the US Air Force launched a program for a subsonic tactical support warplane able to carry a large warlord in the primary anti tank role. Prototypes were ordered from Fairchild Republic and Northrop. A YA-10A first flying in May 1972 the YA-10A was evaluated competitively against the YA-9A, and declared winner of the competition in 1973. The Thunderbolt II was designed as a low coast type, and therefore lacks all weather capability and relies on the pilot's head up display for accurate weapon delivery. Total production was 723 aircraft designed specifically to survive against Soviet battlefield air defense and knock out Soviet armor. Survivability was provided by widely separated engines, a titanium armor bath for the pilot and primary systems, and multiple redundancy of the structure and systems. Offensive capability was provided by the GAU-8/A Avenger seven barrel cannon firing depleted uranium projectiles, and a large load of ordnance (including six Maverick air to surface missiles) carried under the fuselage and wings. Despite the type's protective features and low level agility, there are now serious doubts about the A-10s survivability because of its very low speed and comparatively large size.