Marines of the 22nd Marine Expeditionary Unit (22nd MEU) are led to a Marine Medium Helicopter Squadron 261 (HMM-261) CH-46E Sea Knight helicopter aboard the amphibious assault ship USS SAIPAN (LHA 2) during a rehearsal for Operation Sharp Edge. The SAIPAN is on station off the coast of Liberia

The United States Marine Corps traces its roots to the Continental Marines of the American Revolutionary War, formed by a resolution of the Second Continental Congress on 10 November 1775. That date is celebrated as the Marine Corps's birthday. Throughout the late 19th and 20th centuries, Marine detachments served aboard Navy cruisers, battleships, and aircraft carriers. About 600,000 Americans served in the U.S. Marine Corps in World War II, performed a central role in the Pacific War. The Pacific theatre battles saw fierce fighting between Marines and the Imperial Japanese Army. The Battle of Iwo Jima was arguably the most famous Marine engagement of the war with high losses of 26,000 American casualties and 22,000 Japanese. By the end of WWII, the Corps expanded totaling about 485,000 Marines. Nearly 87,000 Marines were casualties during World War II (including nearly 20,000 killed), and 82 were awarded the Medal of Honor. The Korean War saw the Corps expand from 75,000 regulars to a force of 261,000 Marines, mostly reservists. 30,544 Marines were killed or wounded during the war. During Vietnam War Marines evacuated Saigon. Vietnam was the longest war for Marines. By its end, 13,091 had been killed in action, 51,392 had been wounded. Marines participated in the failed 1980 Iran hostage rescue attempt, the invasion of Grenada, the invasion of Panama. On 23 October 1983, the Marine headquarters building in Beirut, Lebanon, was bombed, causing the highest peacetime losses to the Corps in its history. 220 Marines and 21 other service members were killed. Marines liberated Kuwait during the Persian Gulf War, participated in combat operations in Somalia (1992–1995), and took part in the evacuation of American citizens from the US Embassy in Tirana, Albania. Following the attacks on 11 September 2001, Marine Corps, alongside the other military services, has engaged in global operations around the world in support of War on Terror. Marines were among first sent to Afghanistan in November 2001. Since then, Marine battalions and squadrons have been engaging Taliban and Al-Qaeda forces. U.S. Marines also served in the Iraq War.

• History - 22nd Marine Expeditionary Unit