So what did the Japanese do with military plants? Just retool them for civilian purposes?
Japanese industry in the early 20th century was controlled by a business group known as the zaibatsu (財閥), which was formed by the Meiji Emperor in the late 1800s in order to kickstart Japan's industrialization, and then switched over largely by the Showa Emperor (Hirohito) to military production.
After the war the zaibatsu were broken up by SCAP and MacArthur, but soon after the peace treaty the companies that had formed the zaibatsu re-formed, and the plants they had before the end of the war were rebuilt. One big difference was that while the pre-war zaibatsu were vertical monopolies, the post-war replacements were more like horizontal oligopolies, known as keiretsu (系列); they were still manipulated by the government, but for the purposes of building first an export-driven economy, then a consumer-driven economy.
Most Japanese companies today find themselves behind the curve in terms of both innovation and market share; South Korean corporations have been more innovative over the last generation, while Chinese corporations with their cheap labor and export-driven economy (the same thing the Japanese did in the 50s and 60s) have taken over more market share. I really can't point to a Japanese corporation that has figured out how to get out of this dilemma--with the possible exception of Nissan, which has done it by going all-out global. Lots of other Japanese firms, like Toyota, Sumitomo, and Mitsui, have tried, but with less success, for different reasons individual to each.