The unified company was known as Mitsubishi Heavy Industries (MHI), and was the largest private company in Japan.[12] 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.[13]