At 29 years old, Peter entered the United States Marine Corps. on March 30, 1942. He served in active duty from April 4, 1942 to January 23, 1946 in World War II, and September 20, 1951 to April 20, 1957 in the Korean War. He was in the reserve for the period between his active duty.

Serving in the Pacific Theater of World War II, Peter fulfilled his combat correspondent duties by traveling into battle with his fellow Marines. He wrote over 300 new stories about these battles, which were published in newspapers across the country.

Peter, like his war correspondent counterparts, served a variety of capacities when not writing, including performing first aid on wounded soldiers, filling in as gunner on flights to islands, and dropping mail to soldiers located on Iwo Jima. For these duties he earned a Bronze Star.