I believe it's the: RB-1 Conestoga
The RB-1 Conestoga was a twin-engine, stainless steel cargo aircraft designed for the United States Navy during World War II by the Budd Company of Philadelphia, Pennsylvania. Although it did not see service in a combat theater, it pioneered design innovations in American cargo aircraft, later incorporated in modern military cargo airlifters.
The prototype first flew from the Budd Red Lion Factory Airfield in Philadelphia, Pennsylvania on 31 October 1943, piloted by Guy Miller. The prototype had a takeoff run when empty of just 650 feet (200 m), and could carry a maximum payload of 10,400 pounds (4,700 kg) with a takeoff run of 920 feet (280 m).[2] However, the aircraft demonstrated greater than expected fuel consumption; the range with a standard payload was only 700 miles (1,100 km), 650 miles (1,050 km) with a maximum payload. Three prototype aircraft: NX37097, NX41810, and NC45354 were built; one was used for testing radio equipment, while the other two were used for flight test evaluations. During testing, a few aircraft had difficulty with the simultaneous deployment of the right and left landing gear. With the same engines as the C-47, but 3,000 pounds (1,400 kg) heavier (empty), the aircraft was relatively underpowered; it was reportedly said that for an aircraft built by a railroad car company, it indeed handled like one.