Forty ships and submarines representing 13 international partner nations steamed in close formation during a “group sail” Thursday in Rim of the Pacific exercises.

Twenty-six nations, more than 40 ships and submarines, more than 200 aircraft, and 25,000 personnel are participating in RIMPAC from June 30 to Aug. 4, in and around the Hawaiian Islands and Southern California.

Training with other nations for combat and humanitarian assistance in times of disaster has been a focus with the United States increasingly needing to rely on partner nations for security in the region.

Aircraft carrier operations off Hawaii have involved hunting for and defending against mock-enemy submarines, while amphibious ship-to-shore drills will include a big beach assault at the Kaneohe Marine Corps base Saturday.

RIMPAC 2016 is the 25th exercise in the series that began in 1971.