Photo/IllutrationA Maritime Self-Defense Force ship provides fuel to a Pakistani destroyer in the Arabian Sea in 2007 under a special measures law to combat terrorism. (Asahi Shimbun file photo)

Maritime Self-Defense Force vessels provided fuel at least 17 times to U.S. Navy ships in the Sea of Japan guarding against possible ballistic missile launches by North Korea in 2017, government sources said.

The refueling mission is based on an Acquisition and Cross-Servicing Agreement (ACSA) reached between Japan and the United States after contentious national security legislation took effect in March 2016. The new security laws allow for greater cooperation between the SDF and U.S. military and opened the door for Japan’s exercise of the right to collective self-defense.

The security legislation also allows for exchanges of fuel and other supplies, including ammunition, under certain conditions, such as a survival-threatening situation against Japan.

According to the sources, the MSDF’s Mashu fuel ship and other vessels provided about 5,536 kiloliters of fuel to U.S. Navy Aegis ships patrolling the Sea of Japan between May and December 2017.

The MSDF ships also supplied fuel to other MSDF vessels in the same waters.

The vessels were monitoring for possible ballistic missile launches by Pyongyang. In 2017, North Korea fired missiles on 15 different occasions.

The refueling allows U.S. Navy vessels to extend their patrol missions without returning to base. U.S. military officials had long sought MSDF cooperation for refueling, and those requests were reflected in changes made to the SDF Law.

In other cases, both fuel and supplies have been exchanged between MSDF and U.S. Navy ships.

From May to August 2017, the MSDF helicopter carrier Izumo provided fuel and food to U.S. Navy ships during joint training exercises in the South China Sea. The Izumo also received about 2,000 kiloliters of fuel as well as food from U.S. Navy ships.

That exchange shows Japan-U.S. cooperation extends to waters where China has increasingly heightened its military presence.

But the Japanese government still refuses to disclose details about such cooperative efforts on grounds that releasing the information could compromise the activities of the SDF and U.S. military.

Although the new SDF mission of providing protection to U.S. Navy ships started in May 2017, the only detail provided by the government about such missions is the number for all of 2017, which came to two.

SDF ships have previously provided fuel to the militaries of other nations, but special measures laws were required for such missions.

Japan and the United States have also had an ACSA since 1996, but provisions of fuel were previously limited to instances when Japan was under direct military attack or during joint training exercises with the U.S. military and international rescue and relief operations.