As an island nation, Japan has always needed to rely on a powerful naval arm within its military structure. This is as true today as it was in the days of World War 2 (1939-1945) when the Imperial Japanese Navy (IJN) proved itself a formidable and fearsome foe. The modern Japanese Maritime Self-Defence Force (JMSDF) is a far cry from its warrior-minded IJN days but remains a high-advanced and capable fighting force - both on the water and under it.
In support of potential future amphibious-minded operations, particularly across the many island groups challenged now by China and other regional neighbors, the service has invested in three Osumi-class ("Oosumi") warships to serve in the "Tank Landing Ship" (TLS) / "Dock Landing Ship" (LSD) role. Such warships are ultra-critical to amphibious endeavors as they serve to launch land-fighting units from positions offshore and help to establish - and hold - strategic points by way of beachheads. A little over a dozen nations field such dedicated ships with the United States leading the way with eleven (with its San Antonio-class).
The Osumi-class ships are interesting in that their classification as "tank landing ships" is somewhat misleading for they lack the bow-fitted, clam shell-style oversized doors and accompanying unloading ramps common to similar types when disembarking and embarking vehicles. As such, the Osumi-class does not "beach" its forces in the traditional sense, instead, its primary capability is to serve as an offshore dock of sorts and release vehicles and launch helicopters. This no doubt limits the tactical value of the ship class but, in light of Japan's post-World War 2 constitution - which restricts certain defense-building projects - the approach makes sense. Indeed, the Osumi-class was originally drawn up as a compact aircraft carrier for defensive-minded operations but the local Japanese political atmosphere of the time (early 1990s) reshaped the design to become an amphibious support vessel as opposed to an amphibious assault vessel.
The end result is a warship that certainly looks the part of an aircraft / helicopter carrier but lacks much of the capabilities of either type. Its general shape sees a pointed bow and squared-off stern with an unobstructed section of foredeck and aft-deck. The island superstructure splits the design at midships and is offset to starboard while carrying the usual communications, sensors, and radar systems common to modern warships. There is an OPS-14C series air-search radar carried as well as the OPS-28D surface-search unit and the OPS-20 navigation suite. Four Mark 36 SRBOCs (Super-Rapid Bloom Offboard Countermeasures), tube-shaped chaff and decoy launching systems, make up part of the ship's important countermeasures fit. The crew complement numbers 138 with a typical infantry detachment of 300 troops possible. For humanitarian missions, the internals of the ship can be reworked to provide medical care and sleeping/recovery quarters as needed.
Overall external dimensions of the ships-in-class include an overall length of 178 meters with a beam measuring 25.8 meters and a draught of 17 meters. Displacement reaches 8,900 tons under standard loads and this balloons to 14,000 tons under full combat loads.
The aft surface section of the ship is reserved for a pair of medium-lift navy/marine helicopters though no elevator deck or hangar facilities are installed. This restricts the helicopters to the surface and the units need be secured during transport as no shelter is afforded them. All work on the helos must also be done topside. Typically, the spaces are reserved for 2 x Boeing CH-47 "Chinook" medium-lift helicopters of the Japanese Navy or Marine service - though work is ongoing to refit the type to accept the newer Bell-Boeing MV-22 "Osprey" tilt-rotor transports.
Ahead of the island superstructure is a single deck elevator giving access to the lower decks which house vehicles, infantry, and landing craft. At the stern face of the hull is a large loading/unloading ramp used in releasing vehicles and watercraft into the shallows. The warship can house and launch two fully-laden Landing Craft Air Cushion (LCAC) amphibious hovercraft vessels which can help to reinforce Japanese positions by supplying up to ten Main Battle Tanks (MBTs) and up to 1,000 troops.
Installed power includes 2 x Mitsui 16V42M-A marine diesels developing 26,000 horsepower to 2 x shafts. A single bow thruster is used for fine-tuned adjustments. Under full throttle, the vessel can make 22 knots in ideal conditions.
The three ships making up the Osumi-class are JDS Osumi (LST-4001), JSD Shimokita (LST-4002), and JDS Kunisaki (LST-4003). The former pair were constructed at the ship yard at Mitui, Tamano while the latter was completed at Hitachi, Maizuru - this from 1995 until 2000. All are currently assigned to Landing Division 1 at the important (and storied) Japanese Naval port at Kure. The lead ship, JDS Osumi, saw her keel laid down on December 6th, 1995. She was launched for trials on November 18th, 1996, and was formally commissioned for service on March 11th, 1998. All ships are in service as of this writing (2018).
To date (2018), the ships of the class were called-to-action in recovery and humanitarian efforts following the devastating 2011 Tohoku earthquake and subsequent tsunami which claimed nearly 16,000 deaths, injured over 6,150, and caused over 2,500 to go unaccounted. To improve upon the amphibious assault doctrine amidst loosening constitutional restrictions, the JMSDF has invested in the Hyuga-class helicopter carriers (detailed elsewhere on this site) as well as inquired on the purchase of a dedicated amphibious assault ship from the United States, most likely a Wasp-class type. All this is no doubt centered on deterring, or countering, any additional moves by the Chinese across disputed waters and islands in the region.