support for North Vietnam when the U.S. started to intervene, included through financial aid and the deployment of hundreds of thousands of military personnel in support roles. China said that its military and economic aid to North Vietnam and the Viet Cong totaled $20 billion (approx. $160 billion adjusted for inflation in 2022) during the Vietnam War; included in that aid were donations of 5 million tons of food to North Vietnam (equivalent to North Vietnamese food production in a single year), accounting for 10–15% of the North Vietnamese food supply by the 1970s. In the summer of 1962, Mao Zedong agreed to supply Hanoi with 90,000 rifles and guns free of charge, and starting in 1965, China began sending anti-aircraft units and engineering battalions to North Vietnam to repair the damage caused by American bombing. In particular, they helped man anti-aircraft batteries, rebuild roads and railroads, transport supplies, and perform other engineering works. This freed North Vietnamese army units for combat in the South. China sent 320,000 troops and annual arms shipments worth $180 million. The Chinese military claims to have caused 38% of American air losses in the war. The PRC also began financing the Khmer Rouge as a counterweight to North Vietnam at this time. China "armed and trained" the Khmer Rouge during the civil war, and continued to aid them for years afterward. Soviet Union The Soviet Union supplied North Vietnam with medical supplies, arms, tanks, planes, helicopters, artillery, anti-aircraft missiles and other military equipment. Soviet crews fired Soviet-made surface-to-air missiles at U.S. aircraft in 1965. Over a dozen Soviet soldiers lost their lives in this conflict. Following the dissolution of the Soviet Union in 1991, Russian Federation officials acknowledged that the USSR had stationed up to 3,000 troops in Vietnam during the war. According to Russian sources, between 1953 and 1991, the hardware donated by the Soviet Union included: 2,000 tanks; 1,700 APCs; 7,000 artillery guns; over 5,000 anti-aircraft guns; 158 surface-to-air missile launchers; and 120 helicopters. In total, the Soviets sent North Vietnam annual arms shipments worth $450 million. From July 1965 to the end of 1974, fighting in Vietnam was observed by some 6,500 officers and generals, as well as more than 4,500 soldiers and sergeants of the Soviet Armed Forces, amounting to roughly 11,000 military personnel. The KGB had also helped develop the signals intelligence capabilities of the North Vietnamese, through an