Hi, strangely enough, I watched a program on 'The History Channel' about that sub.
It featured the Smithsonian Institute who have recently restored one of the planes.
It explained how the I-400 was to approach the Panama Canal from the East, launch her planes, which were armed with 800lb bombs, and destroy the entrance to the canal. It also explained how after the war, that, and many other subs were scuttled in a place called 'Deep Point 6' which some refer to as the 'Submarine Graveyard'. Apparently the Americans didn't want the technology falling into the hands of the Russians.
A great programme, that I am sure will be repeated, try checking History Channels website for more info.
I found this page for anyone interested in this sub
http://www.pacerfarm.org/i-400/ contains links to models too