The British BAT series of 120 mm anti-tank recoilless rifles used a variety of sighting systems. The original BAT used a purely optical sight. The MoBAT, a lightweight and more portable version, had a 7.62×51mm NATO Bren light machine gun. The final version, the WOMBAT, used the same American Remington M8C .50 in as the M40 recoilless rifle. Both of these were used as gas-operated semi-automatic rifles. The .50 was not, as often assumed, a development of the .50 M2 machine gun using the 12.7×99mm NATO cartridge, but was a shortened 12.7×76mm cartridge.