The Vietnam War, also known as the Second Indochina War, the Vietnam Conflict, and, in Vietnam, the American War, occurred from March 1959[10] to April 30, 1975. The war was fought between the communist Democratic Republic of Vietnam (North Vietnam) and its communist allies and the US-supported Republic of Vietnam (South Vietnam).[11][12] Throughout the conflict the less equipped and trained Vietcong fought a guerilla war and North Vietnamese soldiers fought a conventional war against US forces in the region, using the jungles of Vietnam to spring deadly ambushes whilst the United States used overwhelming firepower in artillery and aircraft to grind down offensives and potential Vietcong bases. In partiular Huey helicopters played a decisive role in air-lifting supplies and when later upgraded with rockets and machine guns took part in the heavy ground conflicts. In 1965 the United States sent in troops to prevent the South Vietnamese government from collapsing. Ultimately, however, the United States failed to achieve its goal, and in 1975 Vietnam was reunified under Communist control; in 1976 it officially became the Socialist Republic of Vietnam. During the conflict, approximately 3 to 4 million Vietnamese on both sides were killed, in addition to another 1.5 to 2 million Lao and Cambodians who were drawn into the war.