3rd Battalion, 3rd Marines, abbreviated as (3/3), was an infantry battalion of the United States Marine Corps, based out of Kaneohe, Hawaii. Known as either "Trinity" or "America's Battalion", the unit normally fell under the command of the 3rd Marine Regiment of the 3rd Marine Division. When fully manned, the unit consisted of approximately 1000 U.S. Marines and United States Navy Sailors. Like most 20th century model infantry battalions of the U.S. Marine Corps, 3rd Battalion 3rd Marines was made up of three rifle companies, Weapons Company and a Headquarters and Services (H&S) company. The battalion was originally formed at Marine Corps Base Camp Lejeune, North Carolina in 1942 and saw action on both Bougainville and Guam during World War II, where it was awarded its first Presidential Unit Citation and Navy Unit Commendation. Marines in the battalion were also awarded one Medal of Honor and seven Navy Crosses during the war.

Operation Starlite was the first major offensive action conducted by a purely U.S. military unit during the Vietnam War from 18 to 24 August 1965. The operation was launched based on intelligence provided by Major general Nguyen Chanh Thi, the Army of the Republic of Vietnam (ARVN) I Corps commander. III Marine Amphibious Force commander Lieutenant General Lewis W. Walt devised a plan to launch a pre-emptive strike against the Viet Cong (VC) 1st Regiment to nullify their threat to the vital Chu Lai Air Base and Base Area and ensure its powerful communication tower remained intact.