As Hartman said, the Japanese code of battle didn't lend itself to submarine warfare very well. That said, they did try numerous missions against the mainland United States and her territories with submarines (like the I-400). There were several mini-subs in the initial attack on Pearl Harbor as well, though they proved very unwieldy and were lost or sunk. I also seem to recall several attempts by the Japanese to release incendiaries over the woodlands in the Pacific Northwest, in an attempt to cause massive fires. On top of all that were missions that were still on paper at the end of the war, many of which included submarines.
Unfortunately, they seemed to see submarines as stealthy means of transport (like getting planes close to the U.S. coast) and less an offensive weapon like the other member countries of WWII.
__________________
|