The B-24D was the first mass-produced series. The B-24D was the Liberator III in British service. It entered US service in early 1942. It had turbocharged engines and increased fuel capacity. Three more 0.50 caliber (12.7 mm) machine guns brought the defensive armament up to 10 machine guns. At (29.76 short tons) maximum takeoff weight, it was one of the heaviest aircraft in the world; comparable with the British "heavies", with fully loaded weights of 30 short tons for (and nearly identical to) the Stirling, the 34 short ton Lancaster and the 27 short ton Halifax.