U.S. Marines from Marine Corps Air Station Miramar spar in the ocean during Marine Corps martial arts instructor course 224-19 at Naval Air Station North Island, Calif., Oct. 9. 2019. The three-week MAI course trains marines to become martial arts instructors. - U.S. Marines from Marine Corps Air Station Miramar spar in the ocean during Marine Corps martial arts instructor course 224-19 at Naval Air Station North Island, Calif., Oct. 9. 2019. The three-week MAI course trains marines to become martial arts instructors.