Throughout the war, the P-47 would undergo constant development. A bubble canopy was added to increase rearward visibility. The final version of the P-47 would be the P-47N, a long-range version with longer wings and fuselage, and an increased fuel capacity. The P-47N was designed to escort B-29s on long missions to Japan for a planned invasion of the Japanese homeland that never came. Production of all versions ended in November 1945. By then, 15,660 P-47s had been built, making it the most produced U.S. fighter of the war. Of those, 1,816 would be the long-range P-47N model. This model would continue to serve with Air Force Reserve and Air National Guard units until the mid-1950s. Republic ranked 24th among United States corporations in the value of wartime production contracts.