Japanese WWII Sen Toku Secret Submarines

In August 2006 I saw a History Channel special on the secret Japanese WWII attack submarine called Sen Toku (secret attack submarine). Prior to seeing this documentary, I had never even heard about this huge submarine because it was intentionally kept a secret by both Japan and US governments. What surprised me is the size of the submarines (Sen Toku I-400 submarine class). Up until the 1960s, these were the largest and most sophisticated submarines built by man. I think to this day they are the only submarines capable of launching bombers. Each of these submarines carried 3 full size naval bombers and spare parts for a fourth.

Here's some additional info about the Sen Toku. Promare 2004 exploration, "Ambitious Ideas" Japan's Submarine Warfare".