Soryu class diesel-electric submarines are built by Mitsubishi Heavy Industries and Kawasaki Shipbuilding Corporation for the Japan Maritime Self-Defense Force (JMSDF). Soryu class is an improved version of the Oyashio class submarine.

The class is also referred to as the SS 2,900t and the 16SS project. Soryu and Unryu were named after the World War II aircraft carriers. Soryu was one of the carriers that participated in the Pearl Harbour attack. Both submarines are home-ported at Kure and operated by Subron 5, S-flotilla-1 of the JMSDF.

Development details

The keel for the first submarine in the class, Soryu (SS-501), was laid down in March 2005. It was launched in December 2007 and commissioned in March 2009. The second submarine Unryu (SS-502) was laid down in March 2006, launched in October 2008, and commissioned in March 2010.

The third submarine Hakuryu (SS-503) was laid down in February 2007 and launched in October 2009 for commissioning in March 2011. The fourth and fifth submarines, Kenryu (SS-504) and Zuiryu (SS-505), were commissioned in March 2012 and March 2013 respectively.

The sixth and seventh submarines in the class Kokuryu (SS-506) and Jinryu (SS-507), were commissioned in March 2015 and March 2016 respectively. The keel for the eighth submarine, Sekiryu (SS-508), was laid in March 2013 and its commissioning took place in March 2017.

The ninth ship Seiryu (SS-509) was commissioned into the JMSDF in March 2018. The tenth and 11th submarines in the class, Shoryu (SS-510) and Oryu (SS-511), were launched in November 2017 and October 2018 respectively. In March 2020, Oryu submarine, the first in the class to feature lithium-ion batteries, was delivered to the JMSDF.

The 12th and final submarine SS-512 was launched in November 2019 and is expected to be delivered in March 2021.

Soryu class design and features

Soryu class carries a hydrodynamic design based on the Oyashio class submarine. It has a larger displacement than any other submarine class in JMSDF’s service. The hull form is made of high tensile steel and is covered with an anechoic coating to reduce the reflection of acoustic waves.

Interiors of the submarine boast acoustic isolation of loud components. The submarine features computer-aided X control planes. The design incorporates highly automated systems.

The submarine is equipped with Stirling engines for increased propulsion performance and underwater endurance. The engine supports superior submerged operations.

The high-performance sonar onboard improves surveillance capabilities. The submarine also features stealth capabilities and enhanced safety measures such as snorkel equipment.

The vessel has an overall length of 84m, a beam of 9.1m, and a depth of 10.3m. The normal draft of the sub is 8.4m. It has a surfaced displacement of 2,950t and a submerged displacement of 4,200t.

Soryu class complements a crew of 65, including nine officers and 56 enlisted members. The submarine can sail at a surfaced speed of 13k and a submerged speed of 20k. It has a maximum range of 6,100nm at 6.5k speed.

Weapon systems

Soryu class is fitted with six HU-606 533mm torpedo tubes for Type 89 torpedoes and UGM-84 Harpoon anti-ship missiles. The Harpoon has a range of more than 124km and speed of 864km/h.

Type 89 is a wire-guided torpedo with active and passive homing modes. It has a maximum speed of 130km/h and can engage targets within the range of 50km. The torpedo can carry a warhead of 267kg.

Sensors / radars

The submarine is equipped with a ZPS-6F navigation or surface search radar. The sonar suite integrates four low-frequency flank arrays, a bow-array, and towed array sonar.

Countermeasures

Soryu features ZLR-3-6 electronic support measures (ESM) systems. There are two 3in underwater countermeasure launcher tubes installed for launching acoustic device countermeasures (ADCs).

Propulsion

Soryu is powered by a diesel-electric propulsion system. Two Kawasaki 12V 25/25 SB-type diesel engines and four Kawasaki Kockums V4-275R Stirling engines provide a total power output of 2,900kW surfaced and 6,000kW submerged.

Soryu is the first submarine of the JMSDF to be equipped with Stirling engines manufactured by Sweden-based Kockums.

Stirling is a silent and vibration-free external combustion engine. The Kockums Stirling air-independent propulsion system onboard reduces the need for frequent battery charging and increases the submerged endurance of the submarine.

The electric propulsion motor drives a propeller through a single shaft. The submarine is also fitted with an X rudder to provide high manoeuvrability to the submarine when operating very close to the seabed. The X rudder configuration was initially developed by Kockums for the Swedish Gotland class. The propulsion system provides a maximum speed of 20k.