3rd Battalion, 5th Marines, along with the 5th Marine Regiment, was first organized on June 8, 1917 as the United States prepared for World War I. The battalion was composed of four companies: the 16th, 20th, 45th and 47th. 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, Muese 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".
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.
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.
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.
During October 1949, 3rd Battalion, 5th Marines was reactivated on Guam. During August 1950, the Battalion deployed to fight against the North Korean army invading the Republic of Korea (South Korea) during the Korean War. The 3rd Battalion fought at such places as the Pusan Perimeter, Inchon, Seoul and Chosin Reservoir. At the close of hostilities, the 3rd Battalion returned to the United States, settling at MCB Camp Pendleton. The battalion's nickname "Darkhorse" sprang from the radio call sign of its commander in Korea, Col. Robert Taplett, who was known as Darkhorse Six.
From June 1966 to March 1971, the 3rd Battalion, 5th Marines fought in South Vietnam during the Vietnam War. They fought in such places as Chu Lai, Da Nang, Quang Nam, Operation Hastings, Operation Union and Union II in the Que Son valley—received a Presidential Unit Citation, the Battle of Hue, An Hoa, Operation Swift in the Que Son Valley—received a second Presidential Unit Citation, and the Ross Combat Base. During the Vietnam War, the unit motto was "consummate professionals".
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, 4th Marine Division, and 4th Tank Battalion. 3/5 distinguished itself in combat operations in Al Wafrah, Kuwait during Operation Desert Storm as 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.
3rd Battalion was deployed for the 2003 invasion of Iraq to oust Saddam Hussein. 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.
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". All eight face additional charges of kidnapping, conspiracy, larceny, assault and housebreaking or unlawfully entering a dwelling. Five of the men are 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.
In June 2006, 3/5 avenged the death of four Scout Snipers who belonged to 2/4 who had been killed on a roof top in Ramadi in 2004. 3/5's mission in Habbaniyah killed the insurgent sniper and driver of a vehicle. The sniper rifle was demilitarized and now resides at the 5th Marines Regimental Command Post.
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. 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.
3/5 was deployed as the Battalion Landing Team 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 former Marine 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 7-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.
To date the battalion has seen eight members decorated with the Navy Cross, and Purple Heart all for gallantry in combat. Two in Korea, five in Iraq, and two in Afghanistan awarded to Sgt Matthew T. Abbate. This is the most for any unit in the Marine Corps.
The battalion's nickname "Darkhorse" sprang from the radio call sign it used in Korea, chosen by Col Robert Taplett, who as the Battalion Commander (CO) during that time had the call sign of "Darkhorse Six." The name fell out of use until 2003; during the training to return to Iraq in 2004 the battalion's CO, Lt Col P J Malay requested use of the Darkhorse call sign as a homage to the Marines bravery in Korea. For the past ten years the nickname has stuck and the battalion now uses it on their unofficial patches.
During the 1980s the name for the battalion was the "Mangudai", named by then C.O. Lieutenant Colonel Jack Kelly, who later went on to be promoted to Brigadier General, Commanding Officer of MCRD, San Diego. Mangudai was the name used by the special forces of Genghis Khan.Sgt Matthew T. Abbate – posthumous recipient of the Navy Cross during Operation Enduring Freedom.
Lance Corporal Christopher Adlesperger – recipient of the Navy Cross for combat in Fallujah 2004.
Sergeant R.V. Burgin – author of Islands of the Damned; Bronze Star for Combat in Battle of Okinawa; recipient of the Purple Heart.
Corporal Jason Scot Clairday – recipient of the Navy Cross for combat in Fallujah 2004.
Corporal Jack A. Davenport – posthumous recipient of the Medal of Honor during the Korean War.
PFC Fernando Luis García – posthumous recipient of the Medal of Honor during the Korean War.
Captain Andrew Haldane – Commanding officer of K company for the Battle of Cape Gloucester and most of the Battle of Peleliu during World War II. Recipient of the Silver Star for leading hand-to-hand combat in an attempt to capture an airfield on Cape Gloucester. A highly revered Marine Officer, Corporal Eugene Sledge's book With the Old Breed is dedicated to him.
Staff Sergeant Elmo M. Haney, served in Company K in the Battle of Guadalcanal, Cape Gloucester and Peleliu.
1st Lieutenant Robert Michael Kelly, son of General John F. Kelly, was killed in action in Sangin, Afghanistan on November 9, 2010.
Jarrett Kraft – recipient of the Navy Cross for combat in Fallujah 2004.
Matt Larsen – creator of the US Army Combatives program.
Sterling Mace – author of Battleground Pacific: A Marine Rifleman's Combat Odyssey in K/3/5.
Staff Sergeant James F McEnery – author of "Hell in the Pacific" A Marine Rifleman's Journey from Guadalcanal to Peleliu.
Staff Sergeant Raymond Plouhar – featured in the film Fahrenheit 9/11.
Laurence Stallings - served in 3rd Platoon, 47th Company during World War I and was wounded during the Battle of Belleau Wood.
Lieutenant General Merwin H. Silverthorn – recipient of the following while in this unit in 1918: Navy Cross, Distinguished Service Cross, Silver Star Medal with oak-leaf cluster, French Croix de Guerre with Silver Star – with diploma, French Fourragere for combat in Aisne-Marne Offensive (Belleau Wood and Chateau Thierry), Aisne-Marne Offensive (Soissons), Marback Sector (Pont-a-Mousson), Meuse-Argonne Offensive (Champagne). Former Assistant Commandant of the Marine Corps.
Corporal Eugene Sledge – author of With the Old Breed.
Colonel Robert Taplett – commander of the battalion, recipient of the Navy Cross for combat in the Chosin Reservoir during the Korean War.
Jeremiah Workman – recipient of the Navy Cross for his valor during the Battle of Fallujah, author of the memoir Shadow of the Sword.
Brian Chontosh - recipient of the Navy Cross during Operation Iraqi Freedom