History of Vietnam since 1945 unstable as no government could keep power for long. There were more coups, often more than one every year. The Communist-run Viet Cong expanded their operation and scored some significant military victories during this period. In 1965, US President Lyndon Johnson sent troops to South Vietnam to secure the country and started to bomb North Vietnam, assuming that if South Vietnam fell to the Communists, other countries in the Southeast Asia would follow, in accordance with the domino theory. Other US allies, such as Australia, New Zealand, South Korea, Thailand, the Philippines, and Taiwan also sent troops to South Vietnam.
Vietnam War saw extensive action during the Vietnam War, and over 600 were deployed with US Forces. Ground forces also had access to B-52 and F-4 Phantom II and others to launch napalm, white phosphorus, tear gas and chemical weapons, precision-guided munition and cluster bombs. The Vietnam War was the first conflict where U.S. forces had secure voice communication equipment available at the tactical level. The National Security Agency ran a crash program to provide U.S. forces with a family of security equipment, code named NESTOR, fielding 17,000 units initially; eventually 30,000 units were produced. However, limitations of the units, including poor