Unryū-class submarine

Project Wadatsumi
Yamatai had successfully tested a nuclear device in 1976, becoming a nuclear weapons state. In the 1980s, it was determined that Yamatai required a credible first- and second-strike capability to properly oppose the communist states in the Escaric Divide. Development of land-based ballistic missiles progressed rapidly with assistance from Chisei, with the Kamikaze-1 being developed in 1981. In 1982, the Imperial Navy began to look into the development of an indigenous ballistic missile submarine under a clandestine study codenamed Project Wadatsumi, which evaluated various ballistic missile submarines around the world through both open and secret means to design a submarine that would fit Yamatai's requirements. Simultaneously, the Kaminami-1 Submarine-Launched Ballistic Missile (SLBM) was also developed, despite Yamatai not having any submarines to launch it at the time.

In 1990, the first design for the Project Wadatsumi ballistic missile submarine had emerged, using nuclear propulsion based on lessons learned from the Mochishio-class submarine, Yamatai's first nuclear-propulsion attack submarine class created in the 1980s. The new class of submarine would be the largest built by Yamatai so far, and would incorporate numerous cutting-edge technologies at the time. Funds for the project were diverted from the simultaneous project to create a new aircraft carrier.

Construction and service
Mitsuhishi Marine Engineering subsequently won the bid for the contract, and construction on the first submarine began in May 1994 at the Noro shipyard. Extreme secrecy surrounded the entire project, and a roof was constructed over the drydock to prevent enemy spy satellites from observing the construction. The second submarine was laid down three weeks later, and the third was laid down in late 1996, intended to be the final boat of the class. After the 1997 Hasukuni earthquake caused severe damage to the under-construction fourth, resulting in its cancellation and scrap, the funds were redirected to the submarine programme and a fourth boat was laid down in 2000.

During this period, the first batch of ballistic missile submarine officers and crews secretly attended training in Chisei in an unprecedented partnership with the Chiseian Royal Navy. After over eight years, the first submarine was launched in 30 August 2002, named Unryū. Empress Kiyono attended the launching ceremony despite her age and deteriorating health.

Declassified government documents in 2020 revealed that the lead boat in the class, Unryū, was deployed to the Crosswind Sea during the 2010 Masukan War, but did not reveal its presence until after the conflict was over.

The entire class underwent minor refits in 2017 to enable them to use the Kaminami-2 upgraded SLBM, after the Kaminami-1 was retired.

Boats in the class
Four Unryū-class submarines have been built between 1994 and 2008.