A version of this article appears in the August 11/18 double issue of Aviation Week & Space Technology.

The Japanese defense ministry has brought forward a proposal to construct at least one large amphibious assault ship that will enlarge the country’s naval aviation capability. The program may also enhance sales prospects for the Bell Boeing V-22 Osprey.

Entry into service for the ship is now targeted for the fiscal year from March 2019; previous plans implied it would be commissioned in the early 2020s, if at all. The ministry will request funding for studies of the ship for the budget year beginning April 1, 2015, Jiji news agency reports. 

Missions include rapid reinforcement of the defenses of Japan’s remote islands, with those actively disputed by China—the Senkaku, or Diaoyu, islands—probably a spur. Tokyo must also consider its claim to the Liancourt Rocks, over which North and South Korea also assert sovereignty.

Operation of an amphibious assault ship in addition to three small Osumi-class vessels now in commission suggests Japanese purchases of additional Osprey tiltrotors, helicopters or both. The fiscal 2014-18 defense plan allows for an order for 17 Ospreys, but that document included no firm plan for new assault shipping nor, presumably, the accompanying aircraft.

The disputed rocks and islands have no airstrips, and the Senkakus are far from the Japanese main territory (see map). Helicopters could fly there from an airport on Miyakojima, an island 200 km (120 mi.) away, but heavy reinforcement would demand sealift, even if the transfer ashore were effected by rotorcraft. While the Japanese navy says it would use air-cushion landing craft and amphibious vehicles only in peacetime or when threats were low, it seems not to have ruled out the possibility of employing vertical lift in the face of enemy opposition.

The proposed schedule for the assault ship suggests the ministry already has a pretty good idea of what it wants to build, because it is giving itself only a year for completing a design. Japanese construction of large warships routinely takes three years. Subject to budget approval, “the ministry of defense will study the required functions and size of such a ship from 2015, with an aim of putting it into service in 2019,” Jiji reports, presumably based on an official briefing.

This represents an acceleration of Japanese planning, because the defense policy that the cabinet adopted in December, the National Defense Program Guidelines, allowed three years for studies up to fiscal 2018 and then a decision on whether to go ahead with construction (AW&ST March 10, p. 46). Because of the ambiguity of Japanese language, it is unclear whether one or more amphibious assault ships are in the offing, but the Japanese navy almost always builds at least two units of every design of fighting ship, even if only one is announced at first.

The defense ministry’s loose specification requires a “multirole ship [or ships] capable of command and control, large-scale transportation and aviation use for amphibious operations.” Defense Minister Itsunori Onodera said on July 8 he would accelerate planning for the program. The plan now looks quite firm. 

Onodera and other officials inspected USS Makin Island in San Diego on July 7. The choice of that Wasp-class ship, with a full-length flight deck, reinforces expectations that Japan wants a design with excellent aviation facilities, potentially supporting the short-takeoff and vertical-landing version of the Lockheed Martin Lightning, the F-35B.

A flat-topped assault ship is not an aircraft carrier, but designers can work in more aviation features than required for amphibious landings, some of which need not be immediately revealed. Moreover, the obfuscating talents of Japanese officialdom could be harnessed to play down a ship’s capacity for tactical airpower.

There would be at least one telltale sign, however. While a ski-jump can be explained as a mere convenience for allies’ F-35Bs, large ships built mainly for amphibious landings never have high speed; they need to devote volume to storage and accommodation rather than unnecessarily powerful machinery. The Osumis are designed for 22 kt., the U.S. Navy’s standard for amphibious shipping, while the combat units of the Japanese navy are generally capable of 30 kt.

The Japanese may see an interesting precedent in the 27,500-metric-ton Italian ship Cavour, which was designed mainly as a carrier with considerable transport capacity. It has loading ramps, troop accommodation and a hangar deck strong enough to accept army vehicles, even tanks. The ship is also capable of 28 kt., partly thanks to the omission of a dock for landing craft, a usual feature of assault ships. 

The construction timetable implied by Jiji’s report looks feasible. IHI Marine United built the two Hyuga-class helicopter carriers in time for commissioning in 2007 and 2009, showing that the industry could handle a two-year interval between large warships. Two Izumo-class helicopter carriers are planned, with the first probably due for commissioning in 2015 and the second possibly in 2017, each after three years of construction. If a design for an assault ship of comparable size can be ready for construction to begin in 2016, then the industry should be able to complete it by 2019.

The vessel may be given a designation less aggressive than “assault ship,” says the Asahi newspaper. The disaster relief function could be emphasized, it says.

Despite that, the ministry of defense plans to study assault-ship operations by the U.S. Navy and Royal Navy, neither of which is noted for giving such vessels a primary function of disaster relief. Rather, the main role of their amphibious shipping is, unambiguously, power projection.