In 1960 the South Vietnamese Navy proposed the creation of an Underwater Demolitions Team to improve protection of ships, piers and bridges. Later in the year a navy contingent was sent to Taiwan for UDT training; the one officer and seven men who completed the course became the cadre for a Lien Doi Nguoi Nhai (LDNN), or Frogman Unit, formally established in July 1961. The LDNN, with a proposed strength of 48 officers and men, was given the mission of salvage, obstacle removal, pier protection and special amphibious operations.

Soon after the creation of the LDNN a second unit was formed: Biet Hai,or 'Special Sea Force', paramilitary commandos under the operational control of Diem's Presidential Liaison Office and given responsibility for amphibious operations against North Vietnam. US Navy SEAL (Sea, Air and Land) commando teams began deploying to South Vietnam in February 1962 and initiated in March a six month course for the first Biet Hai cadre in airborne, reconnaissance and guerrilla warfare training. By October, 62 men had graduated from the firstcycle. A planned second contingent was denied funding.

In early 1964 the LDNN, numbering only one officer and 41 men, began special operations against VC seabome infiltration attempts. Six Communist junks were destroyed by the LDNN at Ilo Ilo Island in January during Operation 'Sea Dog'. During the following month the LDNN began to be used against North Vietnamese targets as part of Operation Plan 34A, a covert action program designed to pressure the Ha Noi regime.

In February a team unsuccessfully attempted to sabotage a North Vietnamese ferry on Cape Ron and Swatow patrol craft at Quang Khe. Missions to destroy the Route I bridges below the 18th Parallel were twice aborted. In March most of the LDNN was transferred to Da Nang and colocated with the remaining Biet Hai commandos. During May North Vietnam operations resumed by LDNN teams working with newly trained Biet Hai boat crews. On 27 May they scored their first success with the capture of a North Vietnamese junk. On 30 June a team landed on the North Vietnamese coast near a reservoir pump house. Ile team was discovered and a hand to hand fight ensued; two LDNN commandos lost their lives and three 57mm recoiless rifles were abandoned, but 22 North Vietnamese were killed and the pump house was destroyed.

In July a second class of 60 LDNN candidates was selected and began training in Nha Trang during September. Training lasted 16 weeks, and included a 'Hell Week' in which students were required to paddle a boat 115 miles, run 75 miles, carry a boat for 21 miles and swim 10 miles. During the training cycle team members salvaged a sunken landing craft at Nha Trang and a downed aircraft in Binh Duong Province. Thirty-three men completed the course in January 1965 and were based at Vung Tau under the direct control of the Vietnamese Deputy Chief of Naval Operations (Operations).

In 1965 the LDNN was given responsibility for amphibious special operations in South Vietnam. Maritime operations against North Vietnam were given exclusively to the Da Nang based Biet Haicommandos and Hai Tuanboat crews, both incorporated into the new seaborne component of the STD, the So Phong Ve Duyen Hai (Coastal Security Service or CSS). The CSS, a joint services unit, was headed by an Army lieutenant colonel until 1966, then by a Navy commander. CSS missions focused almost entirely on short duration sabotage operations lasting one night, and had a high success rate. The CSS relied heavily on special operations teams temporarily seconded from other services. Teams on loan from the Vietnamese Navy considered most effective, were codenamed 'Vega'. Other teams came from the Vietnamese Marine Corps ('Romulus') and Army ('Nimbus'). The CSS also controlled 40 civilian agents ('Cumulus') until the mid 1960s. Unofficialy, the term Biet Hai was used for all CSS forces, regardless of original service affiliation. CSS training was conducted at Da Nang under the auspices of US Navy SEAL, US Marine, and Vietnamese advisors. Further support was provided by the CSS's Da Nang based US counterpart, the Naval Advisory Detachment, a component of MACVSOG.

By the mid 1960s US Navy SEAL teams were being rotated regularly through South Vietnam on combat tours. Specialists in raids, amphibious reconnaissance and neutralization operations against the VC infrastructure, the SEALs worked closely with the LDNN and began qualifying Vietnamese personnel in basic SEAL tactics. In November 1966 a small cadre of LDNN were brought to Subic Bay in the Philippines for more intensive SEAL training.

In 1967 a third LDNN class numbering over 400 were selected for SEAL training at Vung Tau. Only 27 students finished the one year course and were kept as a separate Hai Kich ('Special Sea Unit,' the Vietnamese term for SEAL) unit within the LDNN. Shortly after their graduation the Communists launched the Tet Offensive most of the LDNN SEALs were moved to Cam Ranh Bay, where a fourth LDNN class began training during 1968. During the year the Vietnamese SEALs operated closely with the US Navy SEALS. The LDNN SEAL Team maintained its focus on operations within South Vietnam, although some missions did extend into Cambodia. Some missions used parachute infiltration. 

LDNN after Tet

In 1971, in accordance with increased operational responsibilities under the Vietnamization program, the LDNN was expanded to the Lien Doan Nguoi Nhai (LDNN), or Frogman Group, comprising a SEAL Team, Underwater Demolitions Team, Explosive Ordnance Disposal Team and Boat Support Team. Headquarters remained in Saigon. For the remainder of 1971 the SEALs operated in 12 18-man detachments on neutralization operations and raids inside South Vietnam. SEAL launch sites included Ho Anh, north of Da Nang, Hue and Tinh An.

During the 1972 Easter Offensive the SEALs were transferred to Hue to conduct operations against NVA forces holding Quang Tri; after Quang Tri was retaken some of the SEALs went to Quang Ngai to resume VC neutralization operations. After US Navy SEAL advisors were withdrawn in late 1972 the LDNN SEAL Team, now 200 strong, took over training facilities at Cam Ranh Bay; training, however, was cut in half, with only one fifth given airborne training. The SEALs had been augmented by ten graduates out of 21 LDNN officer candidates sent to the US for SEAL training in 1971.

When the Vietnam ceasefire went into effect in 1973 the SEALs returned to LDNN Headquarters in Saigon. At the same time the CSS was dissolved, with the Navy contingent given the option of transferring to the LDNN.

In late December 1973 the government reiterated its territorial claim to the Paracel Island chain off its coast and dispatched a small garrison of militia to occupy the islands. By early January 1974 the Chinese, who also claimed the islands, had sent a naval task force to retake.the Paracels. On 17 January 30 LDNN SEALs were infiltrated on to the western shores of one of the major islands to confront a Chinese landing party. The Chinese had already departed; but two days later, after SEALs landed on a nearby island, Chinese forces attacked with gunboats and naval infantry. Two SEALs died and the rest were taken prisoner and later repatriated.

During the final days of South Vietnam a 50 man SEAL detachment was sent to Long An; the remainder were kept at LDNN Headquarters in Saigon along with 200 new SEAL trainees. During the early evening of 29 April all SEAL dependents boarded LDNN UDT boats and left Saigon; a few hours later the SEALs departed the capital, linked up with the UDT boats, and were picked up by the US 7th Fleet in international waters.

By Ken Conboy      Reference:

Việt Nam Cộng Ḥa Muôn Năm                                                                          Ever the Republic of Vietnam