Mitsubishi's automotive origins date back as far as 1917, when the Mitsubishi Shipbuilding Co., Ltd. introduced the Model A, Japan's first series-production automobile.[5] An entirely hand-built seven-seater sedan based on the Fiat Tipo 3, it proved expensive compared to its American and European mass-produced rivals, and was discontinued in 1921 after only 22 had been built.[6] In 1934, Mitsubishi Shipbuilding was merged with the Mitsubishi Aircraft Co., a company established in 1920 to manufacture aircraft engines. The unified company was known as Mitsubishi Heavy Industries (MHI), and was the largest private company in Japan.[7] MHI concentrated on manufacturing aircraft, ships, railroad cars and machinery, but in 1937 developed the PX33, a prototype sedan for military use. It was the first Japanese-built passenger car with full-time four-wheel drive, a technology the company would return to almost fifty years later in its quest for motorsport and sales success.[8] A 1937 Mitsubishi PX33 on display at theMondial de l'Automobile in September 2006. Immediately following the end of the Second World War, the company returned to manufacturing vehicles. Fuso bus production resumed, while a small three-wheeled cargo vehicle called theMizushima and a scooter called the Silver Pigeonwere also developed. However, the zaibatsu (Japan's family-controlled industrial conglomerates) were ordered to be dismantled by the Allied powers in 1950, and Mitsubishi Heavy Industries was split into three regional companies, each with an involvement in motor vehicle development: West Japan Heavy-Industries, Central Japan Heavy-Industries, and East Japan Heavy-Industries.