The P-47 Thunderbolt, built by Republic Aircraft, was one of the mainstay fighters of the US Army Air Corps in the latter part of World War II and was the largest single-engine fighter of its time, with its later M/N version ranking among the fastest propeller fighters of the Allies. Apart from being slightly underpowered at low and medium altitudes, the P-47's huge engines and 3.65 metre diameter propellers allowed it to carry more anti-aircraft firepower, heavier armour, and more small bombs for ground attack missions. The P-47 is the most produced U.S. warplane, with 12,602 D-models, the world's largest production run of a single type of military aircraft. In addition to the US Army Air Forces, other allied air forces also used P-47s. The P-47 was nicknamed the "Water Tank" by aircrews at the time as it was significantly larger than other aircraft.