The U.S. escalating involvement and its first troops sent to Vietnam likewise increased Soviet interest in Vietnam remarkably. Leonid Brezhnev signed a defense treaty with Hanoi during a meeting with the Lao Dong Politburo and NVA commanders in February 1965 and Soviet aid began flowing to North Vietnam since then.
One of the main contributions of the Soviet Union was providing early warning of B-52 bomber raids. Soviet ship would detect the flights of B-52s from their bases in Guam and Okinawa and warn COSVN, the headquarters in Hanoi that would relay the approach of B-52s to their air command and anti-aircraft forces. Reportedly, not a single North Vietnamese military or civilian leader was killed by B-52 raids between 1968 and 1970. Soviet forces also shot down the first U.S. planes over Thanh Hoa in August 1965.
The Sino-Soviet split saw Hanoi siding more closely with Moscow. In November 1968, the USSR and North Vietnam signed a new set of military and economic agreements whereby they would supply North Vietnamese forces with planes, tanks, small arms, helicopters, artillery, anti-aircraft missiles, medical supplies and other military equipment to reinforce their defense.
However, no Soviet troops directly participated in combat since 1966 as the North Vietnamese forces had been trained to handle the Soviet equipment. Their advisers were not even told of North Vietnamese operations in South Vietnam as the Viet Cong planned and conducted them independently.
The Soviet Defense Ministry acknowledged in 1991 that 3,000 troops were sent to Vietnam in which 13 were killed.
Both Indochina wars lasting from 1946 until 1975 ended up with Vietnamese communist’s victory over the two world powers. However, without considerable amounts of military and economic support provided by the PRC at first and later the Soviet Union, the outcome would mostly like have been different.
North Korea had provided North Vietnam both political and military support including sending military advisers in the early stage of the Vietnam War due to the close Ideology between Hanoi and Pyongyang. However, they did not actively involved in the conflict until early 1967 after their ruling Workers Party approved the decision in October 1966.
The participation of North Korean forces in the Vietnam War was rather limited compared to their South Korean counterparts. While South Korea sent a total of 313,000 soldiers between 1965 and 1973 to South Vietnam, North Korea only sent in a fighter squadron to North Vietnam in early 1967 to back up their air defenses in the city of Hanoi. The fighter squadron stayed through 1968 and 200 pilots was reported to have served in the conflict in which at least fourteen were killed. In addition, there were at least two anti-aircraft regiments, two million sets of uniforms, ammunition and other weapons sent to North Vietnam as well.
Overall, North Korea’s participation in the Vietnam War was rather restricted due to the guerrilla nature of fighting and limited resources that North Korea was willing to commit.
Similar to most communist allies, Cuba has not officially revealed its secret support to North Vietnam and that its role in the Vietnam War remains mystery. However, the Republic of Cuba under the leadership of Fidel Castro reportedly provided doctors, military advisors and engineers who engaged in widening the Ho Chi Minh trail.
There were also a number of alleged Cuban agents involved in torturing some 19 American POWs, leading to one death, in what becomes known as the “Cuba program”. This is reported by many POW survivors, notably Senator John McCain through his book Faith of My Fathers in 1999. Nonetheless, Cuban leader Fidel Castro denied all these accusations in an article published by his Communist Party newspaper Granma in 2008. Castro himself led a delegation to Hanoi and then visited Quang Tri, which was held by North Vietnamese forces during the Eastern Offensive, on September 15 and 16, 1973 to show his support to the North Vietnamese government.
II. Anti-Communist Allies
Please read more on part two.