As an island nation, it behooves Japanese authorities to provide its people with a powerful naval fighting force made up of multi-mission surface warships and submarines. The Japanese navy - represented as the Japan Maritime Self-Defense Force (JMSDF) - is the branch called upon to defend Japanese political interests in the unsettled Asia-Pacific region. With the growing power of the Chinese - particularly in its own naval branch - further responsibility falls on the Japanese government and the JMSDF to protect its claims as well as vital shipping lanes of this part of the world.
The Oyahio-class of diesel-electric submarines was developed in the early 1990s, seeing construction begin in 1994 and complete in 2008. This initiative resulted in an 11-strong fleet of modern boats for the JMSDF led by JDS Oyashio (SS-590). Oyashio saw her keel laid down on January 26th, 1994 at the Kawasaki Shipyard at Kobe and was launched on October 15th, 1996. She was then officially commissioned on March 16th, 1998. The vessel, along with her ten sister boats, remains an active presence in the JMSDF underwater fleet.
As a diesel-electric-powered submarine, Oyashio is equipped with a hybrid propulsion system which enables both surface and underwater traveling in one complete package. This arrangement includes 2 x Kawasaki 12V25S diesel engines, 2 x Kawasaki alternators and 2 x Toshiba motors. Her diesel systems generate up to 3,400 horsepower while the other propulsion components allow for 7,750 horsepower to be achieved. When surfaced, the vessel can make headway at 12 knots and this is drastically increased during submerged travel to 20 knots. Unlike nuclear-powered submarines, range of diesel-electric types is inherently more limited and limited further still by the available food stores for the crew - usually running up to 1.5 months. The entire crew complement numbers 70 personnel including 10 officers operating in designated shifts.
As an attack-minded submarine, Oyashio is outfitted with 6 x 533mm torpedo tubes serving Type 89 torpedoes or UGN-84 Harpoon anti-ship missiles or a combination of the two based on mission requirements. Some 20 reloads can be carried of each weapon type, or a mixed offering of the two.
Sensors and processing are handled by a Hughes/Oki ZQQ-6 series hull-mounted sonar array. There are also arrays mounted along the flanks of the boat and a towed array can also be released when required. Search/tracking is provided through a JRC ZPS 6 series I-band search radar system.
All of the eleven Oyashio-class boats come under the Project No. S130 heading. The class includes Oyahsio (SS-590) as the lead ship followed by Michishio (SS-591), Uzushio (SS-592), Makishio (SS-593), Isoshio (SS-594), Narushio (SS-595), Kuroshio (SS-596), Takashio (SS-597), Yaeshio (SS-598), Setoshio (SS-599) and Mochishio (SS-600).