The Infiltration of the Tian Shan Mountain Base was a mission conducted by John "Soap" MacTavish and Gary "Roach" Sanderson in the Tian Shan Mountain Range, Kazakhstan. Task Force 141 discovered that Ultranationalists acquired a downed American satellite; Soap and Roach were ordered to acquire the ACS module to ensure Russia can gain no useful information or advantage from the satellite.
Ultranationalist opinion towards Western powers caused a Russian desire for war against the United States. Russia acquired an American satellite and sent it to a Russian base in Kazakhstan, a CSTO ally. In order to prevent Russia from learning important information from the American satellite, Shepherd sent Soap and Roach to the base in order to acquire the satellite's ACS module and escape.
Soap and Roach wait on a ledge near the base until a Russian jet flies overhead. When the two approach Russian forces, Soap informs Roach on the operation of the Heartbeat Sensor. Soap moves onto a higher ledge while Roach plants C4 on the base runway. Soap and Roach meet up when entering the building housing the downed satellite. Soap inspects the satellite as Roach searches the upper level for the ACS module. When Roach takes the ACS module, Soap is taken hostage by Base Commander Petrov. Petrov orders Roach to reveal himself and surrender, or Petrov will execute Soap. Soap reminds Roach of the C4 planted at the runway, which Roach quickly explodes. Soap and Roach neutralize Petrov's team and take control of snowmobiles. The two operatives are followed into a forest by other Russians on snowmobiles and a helicopter. Eventually, the two reach safety near a Kazakh base and extract with Kilo Six-One.
The operation was yet another incident that pushed Russia closer to war. Once World War III began, the Russians used their knowledge of the ACS system to trick American forces into thinking Russia was attacking the West Coast. In actuality, Russia was invading the East Coast, starting the Invasion of Virginia.