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 , and could carry a maximum payload of with a takeoff run of . However, the aircraft demonstrated greater than expected fuel consumption; the range with a standard payload was only , with a maximum payload. 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 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. At the Budd factory and airfield in Philadelphia, Pennsylvania, there were construction delays due to cost overruns and problems with stainless steel fabrication. By late 1943, aluminum production had been increased with the construction of new processing facilities, and other more conventional cargo aircraft (such as the
Curtiss C-46 Commando and the
Douglas C-47 Skytrain) were being produced in large numbers. This caused the Army to cancel its order for the C-93 and the Navy to reduce its RB-1 order from 200 to 25, of which 17 were delivered in March 1944. On 13 April 1944, during a
Naval Air Training Command (NATC) evaluation flight of RB-1 prototype U.S. Navy
NX37097 at
Patuxent River NAS, Maryland, the aircraft crashed, killing one of the crew. The aircraft was damaged beyond repair and written off, but the pilot reported that the stainless steel construction of the aircraft contributed to saving his life. Production RB-1 aircraft never entered squadron service with the Navy, but a few were briefly used by
Naval Air Stations as utility aircraft. With only 17 aircraft in inventory, the RB-1 was not feasible to maintain on the active list, and it was retired from U.S. Navy service in early 1945. The extant RB-1s were then transferred to the
War Assets Administration (WAA) to be sold as war surplus. In 1945, the WAA sold 12 Conestogas to the
National Skyway Freight Corp for $28,642 each (equivalent to ${{Inflation|US-GDP|28642|1945 The seven remaining National Skyways aircraft were used to transport a variety of cargo, shipping fruit and furniture from its base in
Long Beach, California. Pilots reported that the Budd transports were temperamental; in particular, exhaust stacks kept falling off and causing engine fires.There were three more crashes of Conestogas while in service with National Skyway Freight, one each in
Virginia,
New Mexico, and
Michigan. The crash in Virginia was a belly landing at a country club brought on by fuel exhaustion following weather-related problems. The Albuquerque, New Mexico crash was due to a downdraft during a snow storm, from Albuquerque. Pilot and copilot were killed when they were thrown through the windshield and the aircraft skidded over them; the flight engineer survived. In 1947, the U.S. Army (and later the U.S. Air Force) gave National Skyway Freight a large contract for trans-Pacific freight, for which it leased military aircraft. The company changed its name to
Flying Tiger and replaced the RB-1s with C-47s for its U.S. freight routes; the RB-1s were sold off to other buyers. One of these aircraft, a prototype RB-1, "NC45354" was sold to the
Tucker Motor Company to transport its demonstration
1948 Tucker Sedan to auto shows around the U.S.; it was reportedly later abandoned at an airfield in Oakland, California after repeated mechanical troubles.
Brazil A Brazilian regional airline, VASD (Viação Aérea Santos Dumont), which commenced operations on 18 January 1944, with a Budd RB.1 Conestoga and two
Catalinas – all formerly owned by a rubber corporation. The Conestoga (civil registration PP-SDC), was named
Tio Sam ("Uncle Sam"). After a crash landing on 4 January 1947, with the undercarriage partially lowered, at
Campo dos Afonsos, it was written off and scrapped. ==Surviving aircraft==