The I-403 was the pride of the Japanese Navy during World War II. It was on a mission when it came under fire from a submarine of unknown origin, and had more advanced weaponry than the I-403. Captain Shinguji feared that he could not win the battle, and had his crew quickly evacuate the ship. The Mu Empire later recovered the ship, along with the plans for the proposed super submarine, Gotengo.
- In real life, the I-403 was the third planned boat of the I-400-class of submarine aircraft carrier, the same type as it is in the film. However, the real I-403's construction was cancelled after only a month.