Space Carrier Blue Noah (1979)

Year 2052. The Gothams, an alien race, attack Earth. Most of the human population is destroyed. The Gotham's moon, a military battle station, becomes Earth's second moon. A submarine, Blue Noah, is Earth's last chance against the Gothams. Blue Noah has the ability to become a spaceship, but must reach N9, Bermuda, in order to do so. Blue Noah leaves N1, Japan, and sets to cross the Pacific, not knowing whether or not N9 still exists. Many sea battles are fought along the way. 27 episodes, 20 minutes each.