Extensive real estate redevelopment?
EDIT: Apparently it was for his work in developing the post-war Self-Defence Air Force. Although some rumours persist that it was as a return favour for the US giving Minoru Genda (of Pearl Harbor fame) the Legion of Merit, which in turn likely had a lot to do with him choosing the F-104 Starfighter over the F-11 Super Tiger for the JSDAF, which was a real murky mess involving underworld figures and a lot of bribery.
http://en.wikipedia.org/wiki/Lockheed_bribery_scandals