On This Day - What happened 21 August 1937 AD

In September 1937, the Soviet Union and China signed the Sino-Soviet Non-Aggression Pact and approved Operation Zet, the formation of a secret Soviet volunteer air force, in which Soviet technicians upgraded and ran some of China's transportation systems.

Soviets signed a non-aggression pact with China to lend material support, ending China's co-operation with Germany.