JASDF KC-767 refueling tanker. Creative Commons photo, Flickr user Yui Kubo.

For nearly a year now, unknown to most outside of government, the U.S. and Japan have been operating under an agreement that allows Japanese aircraft to refuel American ones. Important caveat: it may be only be done during joint exercises.

The Air Self-Defense Force has exchanged a memorandum with the U.S. military enabling SDF tanker aircraft to refuel U.S. military airplanes midair during Japan-U.S. joint exercises, it has been learned.

Previously, only U.S. tanker aircraft have been able to refuel SDF aircraft during such circumstances, sources said.

According to the ASDF, the memorandum was signed in October last year based on the Japan-U.S. Acquisition and Cross-Servicing Agreement (ACSA), a framework allowing both forces to cooperate on supplies and services.

Currently, they are checking the adaptability of plane models, such as the SDF’s KC 767 tanker aircraft’s ability to refuel U.S. military airplanes.

The ACSA allows reciprocal provision of supplies and services between the SDF and U.S. forces not only during joint exercises, but also when they are responding to emergency situations in Japan or surrounding areas.

However, the Defense Ministry plans to further discuss the circumstances under which the ASDF will refuel U.S. military aircraft during emergencies, such as how the U.S. aircraft are being used, the sources said.

The ASDF started introducing fuel tanker aircraft in 2008 to extend the flight duration of its fighter jets and thus improve their defense capabilities. It currently owns four such fuel tanker airplanes. (Link)

This article in the Asahi states that, according to the MoD, the agreement is not illegal because it does not cover refueling during combat operations, only exercises. Refueling foreign combat aircraft during wartime would be seen as giving aid and assistance to a foreign country, and Japan has a constitutional ban on collective self-defense.

Japan owns 4 Boeing KC-767 tankers, which were ordered in 2001 and delivered between 2008 and 2010. Unlike the Italian version of the KC-767, which has both drogue and boom refueling systems, the Japanese KC-767Js  feature only the boom refueling system. This makes the KC-767J compatible with U.S. Air Force aircraft, but unable to refuel U.S. Navy and Marine Corps aircraft without a boom drogue adapter unit.

Speaking of the midair refueling, Japan’s choice of boom refueling over probe and drogue has some interesting implications for  the F-X program. The F-35 fighter is the only fighter in the competition (F-35A) that uses boom refueling. The Eurofighter Typhoon and Boeing’s Super Hornet use probe and drogue. If either of the latter aircraft were picked, their midair refueling systems would have to be modified to handle a boom system, or the KC-767 would have to incorporate the boom drogue adapter unit.

(Update: The Base Leg Blog‘s Mike Yeo noted on Twitter that it is probably impossible to modify Eurofighter Typhoon and the Super Hornet to accept a boom system, and notes that a better option would be to install wingtip drogues like those on Singapore Air Force KC-135s. It should be noted that the Italian version of the KC-767 tanker has not only a boom but wingtip and centerline hose and drogues.)

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A contributor and editor at the blog War Is Boring, Kyle Mizokami started Japan Security Watch in 2010 to further understand Japan's defenses and security policy.
Kyle Mizokami has 536 post(s) on Japan Security Watch