providing protection from the fire of 406 mm guns to enough protection against 460 mm guns. After these had been reviewed, two of the original twenty-four were finalized as possibilities, A-140-F3 and A-140-F4. Differing primarily in their range ( versus at ), they were used in the formation of the final preliminary study, which was finished on 20 July 1936. Tweaks to that design resulted in the definitive design of March 1937, which was put forth by Rear-Admiral Fukuda Keiji; a range of 7,200 nmi was finally decided upon, and the hybrid diesel-turbine propulsion was abandoned in favor of turbines. The diesel engines were removed from the design because of problems with the engines aboard the submarine tender Taigei. Their engines, which were similar to the ones that were going to be mounted in the new battleships, required a "major repair and maintenance effort" to keep them running due to a "fundamental design defect". In addition, if the engines failed entirely, the armored citadel deck roof that protected the proposed diesel engine rooms and attendant machinery spaces, would severely hamper any attempt to remove and replace them. The final design called for a standard displacement of and a full-load displacement of , making the ships of the class the largest battleships yet designed, and the largest battleships ever constructed. The design called for a main armament of nine 460 mm naval guns, mounted in three three-gun turrets—each of which weighed more than a 1930s-era destroyer. The designs were quickly approved by the Japanese Naval high command, over the objections of naval aviators, who argued for the construction of aircraft carriers rather than battleships. In all, five Yamato-class battleships were planned. Ships Although five Yamato-class vessels had been planned in 1937, only three—two battleships and a converted aircraft carrier—were completed. All three vessels were built in extreme secrecy, to prevent American intelligence officials from learning of their existence and specifications; indeed, the United States' Office of Naval Intelligence only became aware of Yamato and Musashi by name in late 1942. At this early time, their assumptions on the class's specifications were quite far off; while they were correct on their length, the class was given as having a beam of —in actuality, it was about and a displacement of 40,000–57,000 tons (actually, 69,000 tons). In addition, the main armament of Yamato class was given as nine guns as late as July