Despite his avowed Marxist sympathies, Oswald decided to join the US Marine Corps. He idolized his older brother, Robert and wore Robert's US Marines ring. Joining the Marines may have also been a way to escape from his overbearing mother. He enlisted in October 1956, a week after his 17th birthday.
While in the Marines, Oswald was trained in the use of the M1 Garand rifle. Following that training, he was tested in December of 1956, and obtained a score of 212, which was 2 points above the minimum for qualifications as a sharpshooter. In May 1959, on another range, Oswald scored 191, which was 1 point over the minimum for ranking as a marksman.
Oswald, however, was trained primarily as a radar operator, a job that required a security clearance. A May 1957 document states that he was "granted FINAL clearance to handle classified matter up to and including CONFIDENTIAL after careful check of local records had disclosed no derogatory data." Oswald took the Aircraft Control and Warning Operator Course and finished seventh in a class of thirty. The course "...included instruction in aircraft surveillance and the use of radar." He was assigned first to Marine Corps Air Station El Toro in Irvine, California in July 1957, then to Naval Air Facility Atsugi in Japan in September 1957. Although Atsugi was a base for the top-secret CIA U-2 spy planes that flew over the Soviet Union, there is no evidence Oswald was involved in that operation.
Oswald was court-martialled twice: initially because of accidentally shooting himself in the elbow with an unauthorized handgun, and then later for starting a fight with a Sergeant he thought responsible for the punishment he received from his first court-martial. He was demoted from private first class to private, and briefly served time in the brig. Later, he was punished for another incident; while on sentry duty one night in the Philippines, he inexplicably fired his rifle into the jungle.
Small compared to some other Marines, Oswald was nicknamed Ozzie Rabbit after the cartoon character. For his steadfast beliefs, he was also nicknamed Oswaldskovich. In December 1958, he transferred back to the Marine Corp Air Station El Toro. The function of Oswald's unit at El Toro "...was to serveil for aircraft, but basically to train both enlisted men and officers for later assignment overseas." One of Oswald's officers, Lieutenant John Donovan, said that he was a "very competent" crew chief. Oswald subscribed to The Worker and claimed to have taught himself rudimentary Russian. At the El Toro base, in February 1959, he took the Marine proficiency exam in written and spoken Russian and his test results were rated "poor."