fight, but we’re not going to pay for it". Pakistan now turned to China for military aid and the Chinese tank T-59 started replacing the US M-47/48 tanks as the Pakistan Army's MBT (Main Battle Tank) from 1966. 80 tanks, the first batch of T-59s, a low-grade version of the Russian T-54/55 series were delivered to Pakistan in 1965–66. The first batch was displayed in the Joint Services Day Parade on 23 March 1966. The 1965 War had proved that Pakistan Army's tank-infantry ratio was lopsided and more infantry was required. Three more infantry divisions (9, 16 and 17 Divisions) largely equipped with Chinese equipment and popularly referred to by the rank and file as "The China Divisions" were raised by the beginning of 1968. Two more corps headquarters: the 2 Corps Headquarters (Jhelum-Ravi Corridor) and the 4 Corps Headquarters (Ravi-Sutlej Corridor) were raised, also in East Pakistan a corps-sized formation (which was titled as the Eastern Command) was created. President of Pakistan Ayub Khan was President of Pakistan in the all part of the 1960s, but in the last part of the decade, popular resentment had boiled over against him. Pakistan had fallen into a state of disarray, and the long civil unrest in East Pakistan had evolved into a mass uprising in January of the year of 1969. After Ayub Khan had unsuccessful talks with the opposition, he handed over power to Yahya Khan in March 1969, who immediately imposed martial law. When Yahya Khan assumed the office on 25 March 1969, he inherited a two-decade constitutional problem of inter-provincial ethnic rivalry between the Punjabi-Pashtun-Mohajir dominated West Pakistan and the ethnically-Bengali Muslim East Pakistan. In addition, Yahya also inherited an 11-year problem of transforming a country essentially ruled by one man to a democratic country, which was the ideological basis of the anti-Ayub movement of 1968–69. As an army chief, Yahya had all the capabilities, qualifications and potential, but he inherited an extremely-complex problem and was forced to perform the multiple roles of caretaker head of the country, drafter of a provisional constitution, resolving the One Unit question, satisfying the frustrations and the sense of exploitation and discrimination successively created in the East Wing by a series of government policies since 1948. The American political scientist Lawrence Ziring observed : Yahya Khan attempted to solve Pakistan's constitutional and inter-provincial/regional rivalry problems once he took over power from Ayub