By Nicholas P. Brown

(Reuters) – Boeing Co (NYSE:) Co has delivered the first KC-46A airplane to Japan. It was the first such delivery to an American customer.

Under a 2017 contract, the Japan Air Self-Defense Force took delivery. Boeing described the “significant milestone” in U.S.-Japan relations in the Indo-Pacific.

JASDF, the U.S. Air Force, and JASDF originally awarded a contract in exchange for one KC-46A. They have also exercised options on three other jets. Boeing calls the aircraft its top-of-the line refuelling tanker. The plane is fitted with high-tech sensors that allow it to carry passengers and cargo while it refuels other airplanes. 

Nonetheless, performance problems have plagued the KC-46 lines used by U.S. Air Force, with defects in an on-board camera system.

Japan is looking to counter China’s assertive military posture in Asia, and Sunday’s delivery will be a tension-filled moment.

The ruling party of the country, which exceeded all expectations in maintaining a majority at Sunday’s parliamentary elections, has promised to double its defense expenditures as Chinese sentiments grow more sceptical.

Japan’s military strategy focuses on protecting territory at the East China Sea edge. It is currently locked in dispute with China over uninhabited islands.