Complex sentence: He enlisted in the Marine Corps in Cleveland, Ohio, on October 1,1941 when he was 18 years of age and was ordered to Parris Island, South Carolina, where he received his recruit training.
Split into simpler sentences: He enlisted in the Marine Corps in Cleveland, Ohio, on October 1,1941 when he was 18 years of age. Following his enlistment, he was ordered to Parris Island, South Carolina, where he received his recruit training.