In the future the world is taken over by the Ocean Empire. The Earth's only hope lies with the Super 99, a submarine designed by Dr. Juzou Oki.

The story follows Susumu Oki, the chief mechanic of the SS-99 and the adventures he and the other crew members take on the SS-99 to save Earth.

(from ebookjapan):

Anomalies are occurring at the bottom of the sea! In response to the global crisis, the deep-sea exploration vessel "Kurofune" heads for the Japan Trench, but is destroyed by a submarine of the "Helmet Party" that it encounters at a depth of 10,000 meters...

Dr. Oki's son, Susumu, who was on board the "Kurofune," follows in the footsteps of his father and brother who disappeared into the sea with the "Kurogane," and boards the submarine "Super 99" that they left behind! Why was the "Kurofune" targeted? What is the purpose of the Helmet Party? The "Super 99" is now ready to set sail!

The great marine action-adventure manga by Leiji Matsumoto!