In 1983, Japanese Prime Minister Yasuhiro Nakasone promised U.S. President Ronald Reagan that he would make Japan into an “unsinkable aircraft carrier.” The irony was, and remains, that Japan has not possessed an actual aircraft carrier in more than 70 years. But that may soon change. The Japanese government is debating retrofitting a class of destroyers to turn them into aircraft carriers. Beyond answering the expected questions of whether such ships would violate its constitution, Japan will need to decide whether the operational need offsets what is expected to be a significant resource strain.

This dearth of aircraft carriers is a contemporary phenomenon. In the early 20th century, Japan was a global leader in ship-based aviation whose magnum opus in the field, two Shōkaku-class carriers, participated in the attack on Pearl Harbor and every subsequent major naval action of the Pacific War. But Japanese carriers disappeared after the war due to a strong strain of pacifism and constitutional constraints that, together, convinced Japanese leaders to forgo the acquisition of “offensive” weaponry.

Since the Self-Defense Force was established in 1954, the naval service—called the Maritime Self-Defense Forces or MSDF—has built ships larger than some of Imperial Japan’s largest ships. In fact, the newest class of MSDF helicopter destroyers, the 24,000-ton Izumo class, are the largest Japanese ships to enter service since World War II. They look like aircraft carriers with a 248-meter deck, control tower, and large, elevator-served hangar. This is a large ship, bigger than Italy’s Giuseppe Garibaldi and longer than Spain’s new Juan Carlos I.

The two Izumo-class ships in service were built mainly for anti-submarine warfare, with an air wing of 14 helicopters. But they are also ideal command-and-control ships, good for humanitarian assistance and disaster relief, and — given their ability to handle the V-22 Osprey tiltrotor aircraft — potentially valuable in amphibious operations. Since the first Izumo-class ship entered service in 2013, it has been widely rumored that the ship was designed so it could someday be converted into an aircraft carrier.

This rumor may be edging closer to reality. The Ministry of Defense is finishing its revisions of the National Defense Program Guidelines and Mid-Term Defense Plan, which set out Japan’s desired long-term defense posture and a five-year plan to get there. Many of the discussions that feed these documents support the notion that the rumor is based in fact. For example, the government had been debating whether to procure F-35B fighters. Additionally, the government has been studying the feasibility of retrofitting the Izumo-class ships so that F-35Bs can land on it. And in May, the ruling Liberal Democratic Party called for introducing a “multipurpose aircraft carrier” in its proposals for the Guidelines.

Like all things in Japan’s defense debates, new capabilities will inevitably be wrapped up in constitutional questions. Japan’s constitution prohibits it from possessing “war potential.” Because of this, the government refrains from procuring capabilities that go beyond the “minimum necessary level” for self-defense. Anything that does is judged to be violating the constitution. Should Tokyo pursue the aircraft carrier option, critics are bound to raise red flags, and accuse its backers of plotting radical change in Japan’s security policies.

But with the country under increasing duress from Chinese provocations, decision-makers need to ask how Japan can best defend its security priorities. In particular, Tokyo needs to determine how to address and/or deter China’s frequent gray-zone incursions by paramilitary ships that attempt to chip away at Japan’s control of the Senkaku Islands. Data provided by the Japanese Ministry of Defense’s Joint Staff Office shows these incursions are matched by a trend of increasing Chinese aircraft activity in and around Japan’s Southwest Island chain. Japanese pilots are forced to scramble against a growing number of Chinese fighters and bombers. But with a smaller force compared to a growing China, time is not on Japan’s side. This has given rise to the aircraft carrier debate.

Aside from constitutional concerns, Japan’s possible acquisition of an aircraft carrier from the standpoint of its security priorities, boils down to two key issues.

Operational Issues

Japan’s Senkaku Islands, like many islands in the Southwest Island chain, are vulnerable to Chinese provocations, particularly because of their distance from SDF forces. The closest Air Self-Defense Force base is in Okinawa, which is home to the force’s 9th Air Wing. If China made a move on the Senkaku Islands, which is Tokyo’s greatest concern, the 9th Air Wing would likely be its first target. ASDF aircraft on the more distant Japanese islands of Kyushu and Honshu can provide defensive air cover only with the help of aerial tankers. A carrier helps reduce this vulnerability by narrowing the gap between Japan’s air bases and its vulnerable territory. From this perspective, the carrier makes sense, since it enlarges Japan’s defensive range and provides it with some level of resiliency. As an added bonus, it would deepen the operational value of the U.S.-Japan alliance.

Resource Issues

The Izumo-class-turned-aircraft carrier is expected to carry about 10 F-35Bs. One estimate puts the conversion of one Izumo ship at close to $500 million, plus another $1.4 billion to put a dozen F-35Bs on it. That means converting both Izumo-class ships and equipping them with 10 planes apiece would cost about $4 billion. With 2019’s defense budget request at $48 billion, the conversion and equipping alone would account for about 8 percent of Japan’s total annual defense budget—a substantial chunk of the consistently tight budget to ensure 20 F-35Bs have a mobile airfield. Add to that the expected lifecycle costs for both the ships and the aircraft. Together, this may divert vital resources away from other types of capabilities that could also disperse the SDF’s lethality and put its adversaries at risk, at range. And these resource concerns extend to human capital. Because Japan’s population is rapidly declining, introducing new platforms that demand more personnel—whether on the flight deck, in planes, or in maintenance—promises to increase pressure on already strained SDF recruitment.

So What?

Considering both operational needs and resources limitations, does an aircraft carrier for Japan make sense? Given the resource pressures, if Japan is interested in defending its territory, it may be better served by investing in means to bolster island defenses and amphibious units to retake islands. Even establishing a joint operational headquarters to ensure greater jointness among the three SDF services might go a long way to help the SDF better counter Chinese aggression.

If air superiority is the driving motivation, the ASDF may be better served by arming unmanned aerial vehicles. Should Japan be able to base some of these assets on uninhabited islands closer to the Senkaku Islands, it would not only provide much-needed presence to bolster Japanese vulnerabilities, it would be cheaper, require fewer operators and enable Japan to distribute lethality over a wider geographical area.

However, Japan does not have the technology to conduct air superiority missions with unmanned assets. If it wanted this capability, it would have to invest heavily in it, which would likely take years to acquire. This makes retrofitting the Izumo-class appear to be a relatively quick fix in the short-term. But it comes at great cost, because it would lock in a sizeable portion of the defense budget for years to come and strains manpower. Even if this capability was acquired, there is the larger question of whether 20 F-35Bs would be the main factor determining whether Japan can obtain air superiority against a much larger Chinese air force.

Japan faces a rising Chinese threat, and an aircraft carrier could help it maintain air superiority potential missions. But acquiring a carrier would be extremely costly and divert resources from less expensive options. Japan needs to make a decision, and the clock is ticking.