[1]: 44 The campaign was motivated by concerns that China's industrial and military infrastructure would be vulnerable in the event of invasion by the Soviet Union or air raids by the United States.
Its development was motivated by national defense considerations following the escalation of the Vietnam War after the Gulf of Tonkin Incident, the Sino-Soviet Split and small-scale border skirmishes between China and the Soviet Union.
With large projects such as Chengdu-Kunming Railway, Panzhihua Iron and Steel, Second Auto Works, the Third Front Movement stimulated previously poor and agricultural economies in China's southwest and northwest.
For national defense reasons, location choices for the Third Front projects followed the guiding principle “Close to mountains, dispersed, hidden” (kaoshan, fensan, yinbi).
[2]: xiv The "Small Third Front" (xiao sanxian) referred to rugged or remote areas in more major provinces like Shanxi, Anhui, and Hebei.
[3]: 9 In February 1962, Chen Yun had proposed that the Third Five-Year Plan should “solve the problems of food, clothes, and other life necessities” (jiejue chichuanyong).
The preliminary draft for the Third Five Year Plan, of which Deng Xiaoping was a major author, had no provision for largescale industrialization in the country's interior.
[3]: 24 In April 1964, Mao read a General Staff report commissioned by deputy chief Yang Chengwu[3]: 54 which evaluated the distribution of Chinese industry, noted that they were primarily concentrated in 14 major coastal cities which were vulnerable to nuclear attack or air raids, and recommended that the General Staff research measures to guard against a sudden attack.
This evaluation prompted Mao to advocate for the creation of a heavy industrial zone as a safe haven for retreat in the event of foreign invasion during State Planning Meetings in May 1964.
[3]: 4 Subsequently referred to as the Big Third Front, this inland heavy industrial base was to be built up with the help of enterprises re-located from the coast.
[3]: 4 At a June 1964 Politburo meeting, Mao also advocated that each province should also establish its own military industrial complex as an additional measure (subsequently named the Small Third Front).
Other key leadership, including Deng Xiaoping, Liu Shaoqi, and Li Fuchun, did not fully support the notion of the Third Front.
[3]: 7 Mao became concerned that the United States could strike China's nuclear weapons facilities in Lanzhou and Baotou and advocated even more strongly for development of the Third Front.
[3]: 7 In 1965, Yu Qiuli was given the lead role in developing the Third Five Year Plan, consistent with its changing focus to preparations for the possibility that "the imperialists [would] launch an aggressive war against China.
[1]: 179 This principle was motivated by national defense considerations; plants were required to be hidden in the mountains and were not allowed to be geographically clustered to minimize the damage of air strikes.
[3]: 206–207 As Planning Commission Director, Li Fuchun set design rules stating that Third Front projects should not attempt to be "big and complete" or incorporate major administrative, social service, or other buildings not involved in production.
[3]: 12 As the Cultural Revolution ignited leftist extremism, Lin Biao, Chen Boda also replaced Li Fuchun, Peng Dehuai, and Deng Xiaoping as the actual leaders of the Third Front Movement.
[3]: 150 The central Party's efforts to accelerate Third Front work in June 1969 also became entwined with the PLA's enforcement of political discipline and suppression of the factions that had emerged during the Cultural Revolution.
[3]: 150 Those who did not return to work would be viewed as engaging in "splittist activities" (fenlie huodong) which risked undermining preparations to defend China from potential invasion.
[3]: 150–151 The perceived necessity of rushing construction in preparation for foreign invasion, along with constraints on resources, resulted in defects in many Third Front projects.
"[3]: 94 The Party did not attempt to hide the challenges of working on the Third Front, however, and told local officials to "speak clearly about the difficulties, not boast, and not make empty promises.
"[3]: 94 Because Chinese policymakers believed that the risks of invasion from foreign powers were imminent, Third Front workers were instructed to "engage in a race against time with American imperialism and Soviet revisionism.
[3]: 129 Workers themselves often linked their tasks to broader conflicts, for example describing the drilling of tunnels as an act in opposition to "American wolves," thereby advancing "the people of Vietnam's war" with the United States.
[3]: 139 Third Front factories often assigned workers to read the classic Mao speeches Remember Norman Bethune, The Foolish Old Man who Moved Mountains, and Serve the People.
"[3]: 228 The Planning Commission also stated concerns about the amount of Third Front funding leading to neglect of heavy industry elsewhere, as well as insufficient investment in agriculture.
Some Third Front plants moved out of the mountains and caves to nearby small and medium sized cities where the geography and transportation were less difficult.
[3]: 209 As a result, constructing the Third Front was designed to improve China's relative strength in land warfare and bolster its industrial defense capacity.
Regional energy outputs increased in Third Front areas, which also benefitted related sectors like machine building, railroads, and metallurgy.
By 1980, the programs had created a railway grid linking previously isolated parts of western China,[12] in addition to a galaxy of power, aviation and electronic plants, said Zhang Yunchuan, minister of the Commission for Science, Technology and Industry for National Defense.
[3]: 18 Given the formerly secretive nature of the Third Front, Chinese researchers have benefitted from their unique access to archives, oral histories and interviews of participants, grey literature, and classified materials.