The Vertol 107 prototype, N74060, first flew in 1958. Before the US Marines adopted the design as the HRB Sea Knight in 1961, the US Army tested three YHC-1A airframes, but the Army opted for a heavier transport helicopter, the Chinook, which was confusingly designated YHC-1B before becoming the CH-47. This was the first YHC-1A. The HRB and HC-1A designations were unified to CH-46 in 1962. 58-5514 assigned to NASA in 1964. Later NASA 533. Airframe withdrawn in 1975 with 685 flying hours, fate unknown. Photo from: NASA Langley