Japan is actually the second biggest foreign holder of US debt. As of February 2014, Japan held 1.210 trillion of US debt while China held 1.272 trillion.
I am having trouble finding historical data, but what I can find from the 90s indicates that Japan alternated for the top foreign US debt holder with the UK. I am not really sure what data to look for general Japanese foreign investment.
http://www.treasury.gov/ticdata/Publish/mfh.txt
I am having trouble finding historical data, but what I can find from the 90s indicates that Japan alternated for the top foreign US debt holder with the UK. I am not really sure what data to look for general Japanese foreign investment.