In the late 1960s the situation on the Sino-Soviet border became more tense and many new units were sent to Siberia, or formed there, such as the 29th Army. Among these formations was the 11th Guards Motor Rifle Division, which was transferred from Smolensk to Bezrechnaya in May 1968. Thanks to this buildup, Chita became one of the developed cities in Eastern Siberia. In 1988 the District included the 29th Army at Ulan-Ude (5th Guards Tank Division, 52nd, 91st and 245th Motor Rifle Divisions), the 36th Army at Borzya (11th Guards, 38th Guards, and 122nd Guards Motor Rifle Divisions), the 212th Guards District Training Centre at Chita (just renamed from the 49th Tank Training Division), the 150th Training Motor Rifle Division, and the 39th Army, controlling Soviet troops in Mongolia, which had its headquarters at Ulan-Bator and included the 2nd Guards Tank Division, 51st Tank Division, and 12th, 41st, and 91st Motor Rifle Divisions. The Soviet troops in Mongolia were finally withdrawn between 1989 and 1992. Air support to the troops in Mongolia was provided for a time by the 44th Mixed Aviation Corps headquartered at Choybalsan, from 1982 until 1988.