The F-105 was a private venture for Republic intended to replace F-84. Program approved by USAF 1953. Main characteristics were versatility and formidable weaponry (about 13,000 lbs in D and later models); could fly at Mach 2 in straight and level flight. Special weapon could be carried in an internal bomb bay. D prototype flew about same time as first B models produced. D had more advanced electronics, more powerful (by about 20%) engine, and 20-mm M61 Vulcan "Gatling gun" cannon with 1029 rounds. F had complete dual-control system; some modified into G "Wild Weasel" models. Greater part of operational career spent in Vietnam; 1963-8 these aircraft carried out over 75% of assault missions of USAF . For these, F-105 could carry up to 12,000 pounds of external stores and fitted fuel tank in bomb bay. Both Republic and USAF concerned about potential problems of special weapons delivery at supersonic speed. Earlier experience with B-47s at high subsonic Mach resulted in some released bombs striking bomb bay interior due to high internal turbulence and dynamic pressures. Because of this, F-105's nuclear delivery system based on internal carriage of the weapon and ejection by a large hydraulic-piston with about a 30-inch stroke which imparted velocity of 32 fps. Allowed weapon to release clear of adverse air flow in and near aircraft. As aircraft being designed, however, special weapon with "blunt shape" casing was especially tailored for use in F-105. Early drop tests with prototype F-105 showed this shape almost totally stable--even in adverse air flow and high dynamic pressure--and powered ejection not needed. Weapon's trajectory was repeatable over a wide range of release angles and velocities.