The American Republic P-47 Thunderbolt, also known as the Jug, was the largest single-engined fighter of its day. It was one of the main United States Army Air Force (USAAF) fighters of the Second World War. The P-47 was effective in air combat but proved especially adept in the ground-attack role. Its modern-day equivalent in that role, the A-10 Thunderbolt II, takes its name from the P-47.