The U.S. military and Japan’s Self-Defense Forces have begun Exercise Keen Sword 17, 13 days of joint military drills. It is their first since Japan’s new security law took effect in March.

The new law has aroused controversy as it expands the nation’s military role. Japan has sent some 25,000 personnel, 20 vessels and as many as 260 jets. The Americans are deploying about 11,000 soldiers.

The drills are taking place at sites throughout mainland Japan and Okinawa, and also the Northern Mariana Islands. Okinawa will stage a scenario in which the U.S. is at war with a third party and Japan offers its assistance.

Analysts say this is to prepare Japan’s Self-Defence Forces for involvement in similar situations.