The Japan Maritime Self-Defense Force (JMSDF, Kaijō Jieitai) commissioned its third Hibiki-class ocean surveillance ship in a ceremony held on 4 March at Tamano Works, Mitsui E&S Shipbuilding Co, Tamano, southern Okayama Prefecture. Named Aki (with pennant number AOS 5203), the small waterplane area twin hull (SWATH) vessel was inducted into the service’s Ocean Surveillance Division 1 at the Kure naval base in Hiroshima Prefecture shortly after being handed over by Mitsui E&S. Her name is from Aki-nada in the Seto Inland Sea. Aki was laid down in October 2018 at Mitsui Engineering & Shipbuilding, Tamano and launched on 15 January 2020.
The Hibiki class was developed in response to the launch of the Kilo-class submarines by the Soviet Union, and their deployments in the waters near Japan. The Japan Defense Agency announced plans to develop a surveillance ship in 1989. The first Hibiki-class vessel was commissioned on January 23, 1991, and the second, Harima, on March 10, 1992. Hibiki and Harima operate out of Kure, Hiroshima. The United States and Japan reportedly split the costs of operating the Hibiki vessels, which approximately US$20 million per year. As of 2021, the three Hibiki-class ships are Aki (AOS 5203), Hibiki (AOS 5201) and Harima (AOS 5202).
Hibiki-class vessels have a beam of 30 metres (98 ft 5 in), a top speed of 11 knots (20 km/h; 13 mph), and a standard range of 3,800 nautical miles. Each vessel has a crew of 40, including five American civilian technicians, and a flight deck for helicopters to operate off of. They are able to deploy on station for 90 days. The vessels have an AN/UQQ-2 Surveillance Towed Array Sensor System (SURTASS), which is installed in the United States. Data from the sensors is relayed through the Defense Satellite Communications System, and processed and shared with the United States. The data is fed into the Integrated Undersea Surveillance System. Propulsion is provided by four Mitsubishi S6U-MPTK diesel electric engines.