Slowly, steadily Japan is building its naval aviation strength, and with it a latent capacity for local power projection. A third helicopter carrier, launched in August, is due for commissioning in 2015, while a sister ship is planned and probably under construction. In December, Japan decided to take the first steps toward increasing its amphibious capability, which will likely produce at least two ships larger than the current three, with full-length flight decks.

Japan chose the F-35A as its next air force fighter two years ago, so the navy now has a clear option of equipping new amphibious ships with the F-35B, the short-takeoff-and-vertical-landing (Stovl) version of the Lockheed Martin fighter. The Japanese government is adamant that it is not considering the F-35B—but it does not need to do so yet. Japan is on the verge of beefing up its amphibious aviation capacity with an intended order for the Bell-Boeing V-22 Osprey, while a separate program called Navy UH-X will introduce 15 medium or medium-heavy naval utility helicopters, increasing the capacity for assault landings.

Even without F-35Bs and V-22s, Japanese naval aviation is a long way from the late 1990s, when the nearest ships it had to carriers were four anti-submarine destroyers with three helicopters each.

The defense policy adopted by the cabinet in December, called the National Defense Program Guidelines, requires studies until 2018 for new amphibious ship or ships, the Jiji news agency reports. When the studies are complete, a decision will be made whether to go ahead with construction, Jiji says.

Japan disputes ownership of several islands and rocks with China and South Korea; another concern may be defense of larger, inhabited islands over which sovereignty is not in doubt. Rapid movement of soldiers to remote islands is also a consideration in the design of the Kawasaki Heavy Industries UH-X utility helicopter.

Jiji's Japanese-language report is ambiguous about whether one or more amphibious vessels are proposed, but Japan never builds single fighting ships; the fleet has at least two units of every design.

Japan has three Osumi-class landing ships of 14,000 tons full-load displacement. Since the proposed construction includes “excellent operational capability,” something rather larger than the Osumis must be planned. Moreover, the Japanese navy has for many decades consistently built successively larger ships in each category. The new ship would be multifunctional and capable of quickly transporting troops for the defense of remote islands or responding to disasters, such as the 2011 earthquake and tsunami, says Jiji.

Since the Osumis have very limited capabilities to operate helicopters, Japan will very likely want good aviation facilities in its next amphibious ships. That, in turn, is very likely to dictate a flight deck stretching the length of the ship, or nearly so, with an island superstructure offset to starboard.

All this seems to add up to entry into service in the next decade of two LHDs—landing ships with full helicopter facilities and docks for landing craft—of more than 20,000 tons full-load, possibly much more. But it does not necessarily add up to aircraft carriers.

Since the Harrier Stovl attack jet appeared in the 1960s—about the same time as the first amphibious ships with full-length flight decks—people have casually imagined that the latter can become aircraft carriers. It is not so simple, points out Andrew Davies of the Australian Strategic Policy Institute in Canberra, where, a few years ago, similar speculation focused on the forthcoming Canberra-class LHDs of 27,500 tons full-load. An aircraft carrier needs command facilities, communications and radar for intensive air operations. It will usually be much faster than an amphibious vessel, for tactical maneuver and wind over its flight deck. The magazines must be big enough to feed sustained combat aircraft sorties. And the deck must be built for fighters that weigh much more than helicopters and blast it with hot exhaust gas.

Will Japan's next flat-tops have those features, or at least be readily adapted to incorporate them? Probably. The question must at least be on the minds of the navy's leaders and designers, since even a small number of F-35s would be a boon to Japanese operations if land-based airpower were unavailable because of range or airfield damage. A similarly important issue is whether the four anti-submarine helicopter carriers in service or under construction, capable of 30 kt. and already fitted with high-grade command features and sensors, have the physical provisions for F-35B operations.

The first two, Hyuga and Ise, with standard displacement of 14,000 tons and length of 197 meters (646 ft.), are big enough, but only just. Ski jumps can be retrofitted to ships of that size and hangar height is not a problem, since a V-22, taller than an F-35, was lowered into Hyuga in June. But the hangars appear to taper from only about 17 meters width aft to 13 meters forward, and they are obstructed by lifts. The F-35B has a 10.7-meter wingspan and its wings cannot fold, so probably only four or five of the type would fit into each of the ships' hangars, and the fighters could use only the aft lift. Little flight deck parking would be available, and the ships would need space for helicopters, too. Altogether, Japan's first two helicopter carriers are unpromising candidates for the F-35B.

But Japan's next pair, Izumo and its forthcoming sister, both displacing 19,500 tons standard and 248 meters long, are dimensionally comparable to India's Viraat. As the Royal Navy's HMS Hermes in the 1960s and 1970s, that ship operated Buccaneer strike aircraft, as big as F-35s, without the convenience of vertical recoveries. With deck-edge lifts and five meters more width than Hyuga and Ise, Izumo should have much more usable space in its hangar. For the same reasons, its flight deck is much more adaptable to parking F-35Bs and operating them, which altogether looks quite practicable.

The Osumis could never operate F-35Bs, but they would benefit from new rotorcraft. These ships have a large open decks and island superstructures, but helicopters are operated only from the aft end, with the forward space used for vehicle parking. Nonetheless, their airborne capability may be improved with the range and speed of the V-22, which has been tried out on one of the class. Alternatively, helicopters that will be bought for Navy UH-X may offer more flexibility than the twin-rotor, deck-hogging Boeing CH-47 Chinooks currently used.

Since the first unit of the Osumi Class will be 25 years old in 2023, the new program may be intended to replace the Osumis. Such ships can have very long service lives, however, so Japan may intend to increase numbers as well as displacement.

Japan has been considering buying the V-22 for years. “We are actively engaged in the discussions with the Japanese,” says Lt. Col. Eric Ropella, manager of international V-22 programs for the U.S. Marine Corps. He said that should a contract come to fruition, Japan's first batch of aircraft would probably come from production during the final two years of the current, second multi-year contract, and later from a further but unapproved multi-year contract due to begin in 2020.

Meanwhile, the Japanese defense ministry is expected to release a request for proposals for the Navy UH-X requirement in the third-quarter of this year. The functions include replenishment of ships at sea. Although the intended size is described as medium, AgustaWestland is planning to offer its medium-heavy AW101, 13 examples of which are already in Japanese service; Sikorsky is expected to offer a version of the H-60, which has been in Japanese service since the 1990s.

With Tony Osborne in Singapore.