The ultimate development of the cannon-armed light attack aircraft was the small production run in 1944 of the Henschel Hs 129B-3, armed with a modified PAK 40 75 mm anti-tank gun. This weapon, the "Bordkanone BK 7,5", was the most powerful forward-firing weapon fitted to a production military aircraft during World War II. The only other aircraft to be factory-equipped with similar guns were the 1,420 maritime strike variants of the North American B-25 MitchellG/H, which mounted either a M4 cannon, or light-weight T13E1 or M5 versions of the same gun. These weapons, however, were hand-loaded, had shorter barrels and/or a lower muzzle velocity than the BK 7,5 and, therefore, poorer armor penetration, accuracy and rate of fire. (Except for versions of the Piaggio P.108 armed with a 102mm anti-ship cannon, The BK 7,5 was unsurpassed as an aircraft-fitted gun until 1971, when the four-engine Lockheed AC-130E Spectre; equipped with a 105 mm M102 howitzer – entered service with the US Air Force.)