2nd Battalion 5th Marines (2/5 or "Two Five") is an infantry battalion in the United States Marine Corps consisting of approximately 800 marines and sailors. They are based out of Marine Corps Base Camp Pendleton, California and fall under the command of the 5th Marine Regiment and the 1st Marine Division. The battalion has seen combat in World War I, World War II, the Korean War, the Vietnam War and the Gulf War and has deployed many times in support of Operation Iraqi Freedom and the war on terror.

2/5 is the most highly decorated battalion in the Marine Corps, and their motto, "Retreat, Hell!", comes from the French trenches of World War I, when a Marine officer named Lloyd W. Williams was advised by a French officer to retreat and replied, "Retreat? Hell, we just got here!"

2d Battalion 5th Marines was formed on July 1, 1914, and immediately sailed to the Caribbean to quell political turmoil in the Dominican Republic and Haiti. In June 1917, as part of the United States' entry into World War I, the battalion sailed for France with the rest of the 5th Marine Regiment and the American Expeditionary Force. At the time the battalion was composed of four companies; the 18th, 43rd, 51st and 55th. They fought during the Battle of Belleau Wood, Soissons, and the Meuse-Argonne campaign and were twice awarded the French Croix de Guerre with Palm. To this day, members of the battalion wear the French Fourragère representing this award. Following the armistice of 1918, 2d Battalion, 5th Marines was assigned to occupation duties in Germany until their return to Quantico, Virginia, in August 1919.

Beginning in 1920, the battalion began guarding US Mail trains throughout the United States. In 1927, the battalion was sent to Nicaragua to fight bandits and to supervise the 1928 Nicaraguan national elections.

In 1941, the battalion joined the newly formed 1st Marine Division at New River, North Carolina, but later relocated to the west coast of the United States. During World War II the battalion fought in the Battle of Guadalcanal, Battle of Cape Gloucester, Battle of Peleliu, and the Battle of Okinawa. Following the Japanese surrender, the battalion was assigned to occupation duty in Northern China until 1947, at which time they returned to the United States.

Immediately following the 1950 North Korean invasion of South Korea, 2d Battalion, 5th Marines sailed from Camp Pendleton, California, to defend the Pusan Perimeter as a part of the famous "Fire Brigade". The battalion also participated in the landing at Inchon, the liberation of Seoul, the Chosin Reservoir Campaign, and the defense of the East, Central, and Western Fronts before the war was over. From July 1953 to February 1955, 2d Battalion, 5th Marines assisted in the defense of the Korean Demilitarized Zone, after which they again returned to Camp Pendleton.

In April 1966, the battalion deployed to the Republic of Vietnam and served there until 1971. During this time, 2d Battalion, 5th Marines participated in combat operations at Huế, Quế Sơn, Phu Bai, Đông Hà and Phú Lộc. Immediately after their return to Camp Pendleton in 1971, the battalion joined Operation New Arrivals, the relocation of Southeast Asian refugees to the United States.

For the next fifteen years, the battalion deployed regularly as part of the Marine Corps' Unit Deployment Program. In December 1990, 2nd Battalion, 5th Marines sailed for the Persian Gulf in support of Operations Desert Shield / Desert Storm. They were staged in Saudi Arabia and participated in the liberation of Kuwait. During the return transit to the United States, the battalion was diverted to Bangladesh where it provided humanitarian relief as part of Operation Sea Angel.