During the Vietnam War, the ROKMC dispatched the Cheongryeong ('Blue Dragon') brigade to the Republic of Vietnam.
At the request of the United States, President Park Chung Hee of the Republic of Korea agreed to send military units into Vietnam, despite opposition from both the Assembly and the public. In exchange, the United States agreed to provide additional military funds to Korea to modernize its armed forces, totaling about a billion dollars.
The Republic of Korea Army units' Tactical Area of Responsibility were the southern half of the I Corps. The ROK Marine Corps units were deployed with the I Corps alongside US Marines.
Under an arrangement with the USMC, air assets would be provided to the brigade and assigned the same priority for available aircraft as are American units. A team of experts from Subunit One, 1st ANGLICO was dispatched and charged with the mission of keeping an air umbrella over the Blue Dragon Brigade in and out of the field. A two man fire control team was assigned to each ROKMC infantry company at all times.
Initially, the AK-47-equipped Vietcong and NVA outgunned Korean soldiers, since they were armed with World War II-era weaponry (M1 Garand and M1 carbine). However, they soon received more modern weapons from the United States military such as the M16 rifle.
The three main units deployed to Vietnam were the Marine Corps’ (Blue Dragon) Brigade, ROKA Capital Division and the White Horse Division. Various ROK special forces units were also deployed.
Most of the operations never exceeded battalion-size, but they also conducted divisional size operations. Before conducting missions, the South Korean marines laid out their plans much more carefully than their allies, with greater fire discipline, effective use of fire support, and better coordination of sub-units. They also had to their favor the distinguished combat leadership of the company and platoon commanders. During village searches, ROK soldiers would subject the settlement to a series of detailed sweeps while interrogating subjects on the spot. By comparison, American units tended to favor a single sweep followed by a removal of all civilians for screening. Such a painstaking approach certainly paid dividends in terms of weapons seizures and reduced VC activity in ROK areas. Koreans quickly learned pidgin Vietnamese language; for fear that most Vietnamese translators were spies for Vietcong and NVA. Koreans also had better field intelligence than their American counterparts. Koreans conducted counterinsurgency operations so well that American commanders felt that the Korean TAOR was the safest. This was further supported when Vietcong documents captured after the Tet Offensive warned their compatriots to never engage Koreans until full victory was certain. In fact, it was often that the NVA and Vietcong were ambushed by Koreans and not vice versa.
Apparently the ROK Marines were experts at locating enemy weapons caches. The official U.S. report on South Korean participation in Vietnam, entitled "Vietnam Studies: Allied Participation in Vietnam," states that "The enemy feared the Koreans both for their tactical innovations and for the soldiers' tenacity. It is of more than passing interest to note that there never was an American unit in Vietnam which was able to 'smell out' small arms like the Koreans. The Koreans might not suffer many casualties, might not get too many of the enemy on an operation, but when they brought in seventy-five or a hundred weapons, the Americans wondered where in the world they got them. They appeared to have a natural nose for picking up enemy weapons that were, as far as the enemy thought, securely cached away. Considered opinion was that it was good the Koreans were 'friendlies.'"
One of the most notable operations during the Vietnam War was The Battle of Tra Binh Dong in which just under 300 marines successfully defended their base against over 2,400 Viet Cong. Another notable operation is Operation Flying Tiger in early January of 1966; here, the Koreans accounted for 192 Viet Cong killed as against only eleven Koreans.
The U.S. Army manual on Korean participation in Vietnam also states that "[t]he Koreans were thorough in their planning and deliberate in their execution of a plan. They usually surrounded an area by stealth and quick movement. While the count of enemy killed was probably no greater proportionately than that of similar US combat units, the thoroughness with which the Koreans searched any area they fought in was attested to by the fact that the Koreans usually came out with a much higher weaponry count than US troops engaged in similar actions."
A total of 320,000 Koreans served in Vietnam, with a peak strength (of any given time) at around 48,000. About 4,000 were killed. The Korean forces in Vietnam were frequently able to amass a kill ratio of about 25:1 compared to the average American kill ratio of less than 9:1. The U.S Army manual on Korean participation in Vietnam states that" an analysis of an action by Capital Division forces during the period 23–29 January 1968 clearly illustrates the Korean technique. After contact with an enemy force near Phu Cat, the Koreans reacting swiftly...deployed six companies in an encircling maneuver and trapped the enemy force in their cordon. The Korean troops gradually tightened the circle, fighting the enemy during the day and maintaining their tight cordon at night, thus preventing the enemy's escape. At the conclusion of the sixth day of fighting, 278 NVA had been KIA with the loss of just 11 Koreans, a kill ratio of 25.3 to 1. Later in 1968 a Korean 9th Division operation titled Baek Ma 9 (Korean for "white horse," after the White Horse Division) commenced on 11 October and ended on 4 November with 382 enemy soldiers killed and the NVA 7th Battalion, 18th Regiment, rendered ineffective. During this operation, on 25 October, the eighteenth anniversary of the Division, 204 of the enemy were killed without the loss of a single Korean soldier."
The official U.S. military record on South Korean participation in the Vietnam war reads, "In summary, it appears that Korean operations in Vietnam were highly professional, well planned, and thoroughly executed; limited in size and scope, especially in view of assets made available; generally unilateral and within the Korean tactical area of responsibility; subject to domestic political considerations; and highly successful in terms of kill ratio."