 To counteract this weakness, HE ammunition with a reduced load of propellant was used, resulting in a loss of about 100 m/s in muzzle velocity compared to the MK 101, but the rate of fire was increased.The MK 103 entered service in 1943 as the main armament of the Hs 129 B-1 ground-attack/tank-destroyer aircraft, mounted on the underside of the fuselage in a conformal gun pod.The original specification for the MK 103 called for it to fit inside an aircraft's engine mounting (possibly as a "Motorkanone", firing through a hollow propeller hub), but it proved to be too large and heavy to fit into small fighters like the Bf 109.