After the Marco Polo Bridge Incident, the Sino-Soviet Non-Aggression Pact was signed leading to considerable Soviet military assistance to China, including the volunteer squadrons.

In the aftermath of the Wall Street crash of 1929 and the subsequent worldwide economic crisis, the Empire of Japan pursued an expansionist policy against its weakened neighbors in the Far East.

At the time the Soviet Union was undergoing a country wide program of mass industrialization in preparation for a potential war on two fronts (with Germany and Japan respectively).

The establishment of Manchukuo complicated the situation as its territory now housed a colony of 40,000 Soviet citizens working on the Chinese Eastern Railway.

[3] In October 1937, some 450 Soviet pilots and technicians assembled in Moscow, subsequently traveling to Alma Ata to bring 155 fighter aircraft, 62 bombers, and 8 trainers into China.

The Soviets arrived as private citizens and initially wore civilian clothing, the mission remaining a secret even from their closest relatives.

They were instructed to avoid using the term comrade, and in the event of their capture they were to claim that they were former members of the White movement permanently residing in China.

Morale was low and the improvement of the situation was hampered by corrupt officials who bought outdated foreign equipment in return for bribes.

Moreover, the Japanese aircraft were faster and equipped with such novelties as night vision devices and radios, easily outmaneuvering and overpowering any opposition.

At its peak the Soviet Volunteer Group numbered 3,665 personnel, including doctors, drivers, mechanics, meteorologists, cryptographers, radio operators, airfield managers and pilots.

Flying at high attitude and approaching the island from the north, the bombers remained undetected until they dropped their payload, safely returning.

On 28 April, the Japanese launched a massive air raid on the Wuhan military airport with the intent of celebrating the birthday of emperor Hirohito.

As a result, the Chinese turned to the United States, which authorized the creation of the American Volunteer Group Flying Tigers.