Complex sentence: U.S. Navy and Marine Corps SBDs saw their first action at Pearl Harbor, when most of the Marine Corps SBDs of Marine Scout Bombing Squadron 232 (VMSB-232) were destroyed on the ground at Ewa Mooring Mast Field.
Split into simpler sentences: U.S. Navy and Marine Corps SBDs saw their first action at Pearl Harbor. Most of the Marine Corps SBDs of Marine Scout Bombing Squadron 232 (VMSB-232) were destroyed on the ground at Ewa Mooring Mast Field.