After World War II, the American aircraft industry began a search for the DC-3 replacement and Douglas undertook a project to modernize the DC-3. Douglas purchased two second-hand DC-3's and strengthened and stretched the fuselage, added new horizontal and vertical tail surfaces with squared tips, added new squared wing tips and smoother engine nacelles with doors that completely enclosed the landing gear and used more powerful engines, greater cargo capacity and other refinements and was designated the DC-3S.
This new aircraft became known as the DC-3S or the Super DC-3. The Super DC-3 did not sell in the civil market. Unfortunately for Douglas, the project failed because (1) there was an excess of war surplus C-47's/R4Ds available and (2) Convair introduced the more modern, faster and pressurized Convair CV-240. In 1950, Douglas sold the first DC-3S prototype to the U.S. Air Force (USAF); the aircraft was first designated YC-129-DO but later redesignated YC-47F-DO. After testing the aircraft, the USAF decided to purchase the Convair CV-240 and transferred the aircraft to the USN where it was redesignated R4D-8. The USN was impressed with the aircraft and signed a contract with Douglas to convert 100 R4D-5's, -6's and -7's to the R4D-8 configuration later C117-D.
Capital ordered 17 (from American Airlines?) but only flew 3.