World War I

3rd Battalion, 5th Marines, along with the rest of the 5th Marine Regiment, was first organized on June 8, 1917, as the United States prepared for World War I.^[1] The battalion was composed of four companies: the 16th, 20th, 45th and 47th.^[2] Six days later, manned by Spanish–American War and Boxer Rebellion veterans along with a large number of raw recruits, they set sail for France. They participated in campaigns and battles such as Bois de Belleau, Vierzy, Château-Thierry, Pont-a-Mousson, Limey Sector, Fleury, Meuse-Argonne, Blanc Mont, St Michiel, Leffincourt and Soissons. The French Government recognized the young battalion by presenting it the Croix de Guerre along with the Fourragère and changing the name of a French landmark, Belleau Wood, to "Bois de la Brigade de Marine" or "Wood of the Marine Brigade".

Interwar period

In August 1919, the battalion was deactivated following World War I and less than two years later, in May 1921, the 3rd Battalion, 5th Marines was reactivated. For the next several years, men of the 3rd Battalion served in the Caribbean and at home, guarding the U.S. Mail.^[1]

In March 1927, the 3rd Battalion deployed to Nicaragua to help stabilize the government against overthrow attempts by rebel forces. For the next six years, the battalion aided the Nicaraguan government until peace was finally restored. The job done, the 3rd Battalion was once again disbanded in January 1933. In November 1934, the 3rd Battalion was reactivated for the fourth time, only to be deactivated in March 1935.^[1]

World War II

Shortly before World War II in April 1940, 3rd Battalion was again reactivated. The fighting in World War II found the Marines of 3/5 at Guadalcanal, New Britain, Peleliu, and Okinawa. At Peleliu, they were the last Marine battalion to be shipped out before the army took over. In April 1946, their mission accomplished, 3rd Battalion was disbanded and most of the Pacific veterans returned to civilian life.^[1]

Korean War

During October 1949, 3rd Battalion, 5th Marines, was reactivated on Guam. In August 1950 the battalion deployed to fight against the North Korean army's invasion of the Republic of Korea (South Korea) during the Korean War. The 3rd Battalion fought at the Pusan Perimeter, Inchon, Seoul and Chosin Reservoir. It inflicted heavy casualties on Chinese forces at the Battle of Hwacheon. At the close of hostilities, the 3rd Battalion returned to the United States, settling at MCB Camp Pendleton.^[1] The battalion's nickname "Darkhorse" sprang from the radio call sign of its commander in Korea, Colonel Robert Taplett, who was known as "Darkhorse Six".

Vietnam War

From April 1966 to March 1971, the 3rd Battalion, 5th Marines, deployed to South Vietnam during the Vietnam War. They fought in Chu Lai, Da Nang, Quang Nam, Operation Hastings, Operation Union, and Union II in the Que Son valley (where they received a Presidential Unit Citation), the Battle of Hue, An Hoa, Operation Swift in the Que Son Valley (where they received a second Presidential Unit Citation), and Firebase Ross.^[1] During the Vietnam War, the unit motto was "consummate professionals".

Gulf War and the 1990s

In October 1989 the battalion deployed to Panama. They patrolled the jungles and performed reconnaissance for the Army's invasion during Operation Just Cause. On December 1, 1990, the battalion deployed to the Middle East in support of Operation Desert Shield as a Battalion Landing Team with the 5th Marine Expeditionary Brigade. As part of the largest amphibious task force assembled since Vietnam, the battalion was augmented with mobilized Marine Corps Reserve units from 4th Assault Amphibian Battalion; TOW Platoon, 23rd Marines; Company A, 4th Light Armored Infantry Battalion, 25th Marines, 4th Marine Division; and 4th Tank Battalion. 3/5 distinguished itself in combat operations in Al Wafrah, Kuwait, during Operation Desert Storm as a Mechanized Combined Arms Task Force. En route home from hostilities, 3/5 participated in Operation Sea Angel, delivering critical food, supplies, and humanitarian assistance to the cyclone-ravaged country of Bangladesh.^[1]

Iraq War

3rd Battalion was deployed for the 2003 invasion of Iraq. The battalion was again deployed in 2004 to capture the city of Fallujah from insurgents' control. In November 2004, the battalion, along with several other units, participated in Operation Phantom Fury (also known as Al Fajr (Dawn)) and was part of one of the biggest battles in Iraq to that time.^[1]

On June 20, 2006, seven Marines and a Navy Corpsman of Kilo Company were charged with the April 26, 2006, murder of disabled Iraqi civilian Hashim Ibrahim Awad, an event referred to as the "Hamdania incident".^[3][4] All eight faced additional charges of kidnapping, conspiracy, larceny, assault and housebreaking or unlawfully entering a dwelling. Five of the men were accused of making a false official statement.

On May 19, 2006, Darkhorse Marines captured three insurgents responsible for the kidnapping and detention of Jill Carroll, an American journalist with The Christian Science Monitor.^[5]

In June 2006, Lance Corporal Reginal Dutt avenged the death of four 2/4 Marines Scout Snipers who had been killed on a rooftop in Ramadi in 2004. 3/5's mission in Habbaniyah killed the insurgent sniper and driver of a vehicle.^[6] The sniper rifle was demilitarized and now resides at the 5th Marines Regimental Command Post.

Afghanistan

Members of 3rd Battalion, 5th Marines, conducted operations in the Sangin District of Helmand Province, Afghanistan in support of Operation Enduring Freedom between September 2010 and April 2011. The area was handed over by 3rd Battalion, 7th Marines to 3rd Battalion, 5th Marines. Twenty-five of the battalion's Marines were killed in action and 200 were wounded, many losing limbs.^{[7][8][9][10][11][12]}

The 3rd Battalion are using Alternative Energy sources. A couple of forward combat bases use only solar power. One of the Marine foot patrols uses roll-up solar blankets to generate power for their radios and GPS.^[13]

3/5 was deployed as the Battalion Landing Team (BLT) for the 15th MEU. The 15th MEU is deployed with the Peleliu Amphibious Ready Group as a theater reserve and crisis response force throughout the U.S. Central Command and the U.S. 5th Fleet area of responsibility.

In 2013, a Marine veteran Logan Stark of 3/5 released a documentary following the STA (Surveillance and Target Acquisition) platoon of the battalion. Featuring interviews and combat footage from the engagements in Sangin, the documentary named For the 25 memorializes the 25 lost Marines during the battalion's seven-month deployment. Detailing the experiences of the Marines within the platoon, For the 25 recounts the adverse conditions and immense casualties sustained by the battalion and the personal struggles overcome by surviving members of the Scout Sniper platoon.