In the official designation "A6M", the "A" signified a carrier-based fighter, "6" meant that it was the sixth such model built for the Imperial Navy, and "M" indicated Vintage aircraft zero as the manufacturer. The new version was so promising that the Navy had 15 built and shipped to China before they had completed testing. It was owned by an American until Japanese businessman Masahiro Ishizuka purchased it and brought it to Japan last September. Some researchers believe "A6M4" was applied to one or two prototype planes fitted with an experimental turbo-supercharged Vintage aircraft zero engine designed for high altitude. Customers also shopped for. Lockheed Constellation and Super Constellation.