The Japanese aircraft industry, which had been in a very small scale before the Second World War, became the largest manufacturing industry at the end of the War. In this paper, we explored the basis of the growth of the aircraft industry during the war, focusing on No.5 Works of Mitsubishi Heavy Industries Co.. It was made clear that the supply of basic inputs sharply increased. Labor force and “machinery parts” were sufficiently supplied and either of them was not a binding constraint of production. The binding constraint was given by supply of “special parts.” To put it differently, expansion of aircraft production was realized, as the supply of “special parts” increased. Increase of “special parts” supply and still faster increase of “machinery parts” supply were achieved thorough expansion of supplier network both in terms of number of suppliers and the geographical area they were located.