China's support for North Vietnam when the U.S. started to intervene included both financial aid and the deployment of hundreds of thousands of military personnel in support roles. In the summer of 1962, Mao Zedong agreed to supply Hanoi with 90,000 rifles and guns free of charge. Starting in 1965, China sent anti-aircraft units and engineering battalions to North Vietnam to repair the damage caused by American bombing, 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.[199]:135 The Chinese military claims to have caused 38% of American air losses in the war.[16]: China claimed that its military and economic aid to North Vietnam and the Viet Cong totaled $20 billion (approx. $143 billion adjusted for inflation in 2015) during the Vietnam War.[16]: Included in that aid were donations of 5 million tons of food to North Vietnam (equivalent to North Vietnamee food production in a single year), accounting for 10–15% of the North Vietnamese food supply by the 1970s.[16]: