The Tradewind was one of the largest operational flying boats ever built. The 124,000 lb. XP5Y-1 was ordered in August 1946 and was to be powered by four Allison XT-40 six-bladed, counter-rotating turbo-prop engines. The aircraft utilized the latest hull design concepts which produced a long and sleek looking aircraft. Due to engine development problems, the first flight was delayed to April 18, 1950. Besides the XP5Y-1, six R3Y-1 and five R3Y-2 transport aircraft were built. The first six aircraft had side cargo doors while the last five were built as bow-loaders. The bow-loaders increased the personnel load from 80 to 103 in the troop transport mode, and as an air ambulance, the litters were increased from 72 with 8 attendants to 92 with 12 attendants. The loading deck area was 88 feet long and 9 feet wide. The aircraft were primarily used on the Alameda to Hawaii run in 1956 were converted into aerial tankers with four drogue and reel assemblies. The aircraft were operated until April 16, 1958.