Japan takes an iterative approach to submarine construction, with a new submarine class introduced roughly every twenty years that builds upon previous ones. The current class, Soryu, builds upon the older Oyashio class, and the two classes form the entirety of the fleet. Each Soryu features a high degree of automation, reducing crew size to nine officers and fifty-six enlisted men—down ten personnel from the Harushio-class of the mid-1990s.

At 4,200 tons submerged, the nine Soryu-class submarines are the largest submarines built by postwar Japan. Each is 275 feet long and nearly twenty-eight feet wide. They have a range of 6,100 nautical miles and can reportedly dive to a depth of 2,132 feet, or two-fifths of a mile. The Soryu class features an X-shaped tail, reportedly for increased maneuverability in approaching the seabed. This maximizes the sub’s maneuvering room in shallow and littoral waters, particularly the straits in and around Japan that mark key invasion routes.