free and a gearbox separation. One unusual problem was discovered during ground running of the Republic XF-84H Thunderscreech turboprop powered fighter; the special transonic 3-bladed single propeller set up harmonics that proved to be harmful to humans within a certain distance from the aircraft. The major problems of the T40 included gearbox failures, and the propeller control system which used 25 vacuum tubes, and was far from reliable. As the individual power plants were clutched into the gearbox, it was intended in most instances that the aircraft could cruise on one half of the engine and only engage the second power-section when there was need. In practice the system did not work well. Failure to recognize that one of the T38s had failed, and its compressor was devouring power produced by the other section, led to the loss of the first prototype Douglas XA2D-1 and its pilot on 14 December 1950. Operational history The first aircraft to fly with the T40 was the Convair XP5Y-1 patrol aircraft prototype. As flying boat patrol aircraft became redundant, the US Navy changed the role of the aircraft from Anti-Submarine Warfare to Transport. Modifications to the XP5Y-1 (such as provision of air conditioning and pressurisation) produced the Convair R3Y Tradewind, which was to become the only aircraft using the T40 to actually enter service. These large four-engined flying boats served primarily between NAS Alameda and Hawaii during the mid-1950s, (replacing the Martin Mars flying boats). There were numerous problems with the T40s. One resulted in near disaster in 1956, when an R3Y managed to land with a runaway engine, resulting in a collision with a seawall. This event gave the US Navy one more reason to ground the R3Y, which it did soon after. The only other aircraft to be produced in any quantity to be powered by the T40 was the Douglas A2D-1 Skyshark. Of the sixteen examples built, the twelve used for evaluation suffered similar problems to the R3Y. Propeller control problems and gearbox failures were among the more common problems. The T40 was also fitted to the North American A2J-1 Super Savage but the poor performance of the aircraft and continuing difficulties with the engines forced cancellation in favour of the Douglas A3D Skywarrior. The most notable successes of the T40 were in the field of vertical take-off aircraft, being used to power three different types, the Convair XFY-1 Pogo, Lockheed