7 December, 1941

The attack on Pearl Harbor was a surprise attack by Japan on the US naval base in Hawaii. The Japanese intended to prevent the US from interfering with their planned offensive in the Pacific. The attack led to the US entering World War II. 109 Marines were killed or missing in the attack, which was 67% of the total US Marine losses. The USS Arizona's Marine Detachment suffered particularly heavy losses, with only 15 of the 88 Marines on board surviving.

Marines at Pearl Harbor were caught off guard by the attack, but quickly organized a response. They set up anti-aircraft guns and machine guns, and posted Marines on the parade ground and sentry posts. They also formed first aid parties to treat casualties and suppress fires at the Navy Yard. Marines were also sent to Hickam Army Air Field to help with anti-aircraft defense and wreckage clearance.