Douglas developed an improved version, the Super DC-3, with more power, greater cargo capacity, and an improved wing, but with surplus aircraft available for cheap, they failed to sell well in the civil aviation market. Only five were delivered, three of them to Capital Airlines. The U.S. Navy had 100 of its early R4Ds converted to Super DC-3 standard during the early 1950s as the R4D-8, later C-117D. The last U.S. Navy C-117 was retired July 12, 1976. The last U.S. Marine Corps C-117, serial 50835, was retired from active service during June 1982. Several remained in service with small airlines in North and South America in 2006.