In Far East part of the WWII, there had been some foreign troops and mercenaries fighting on China's behave. Japan invaded northeast China which was called Manchuria at the time as early as 1930s. The full scale war against China was started in 1937 when 300,000 Japanese troops landed on the east coast of China at the port city of Shanghai. As we all know, China just went through a revolution and continuous civil war. As a developing nation still under constant wars between the warlords...also between the Nationalist Party and the Communist Party, the whole country was in very poor shape. They did not have the industrial capacity to manufacture any planes nor tanks. Their entire air force were bought foreign planes from various countries, many were outdated too. They had 1 less plane each time they lost one, and these planes were not replaceable during the time of the war. During the Battle of Shanghai, half the Chinese air force were shot down during the two and half months long campaign. The remaining Chinese air force were completely wiped out at the Battle of Wuhan. It was said the last Chinese pilot flying the final fighter plane was able to use the machine guns on the plane to kill hundreds Japanese infantry soldiers in a single fly-by because they were matching in a formation with 4-man column....the Japanese thought there were no more Chinese air force, so they didn't take per-caution. Without air force, the Chinese ground troops were taking heavy casualties against superior firepower of the Japanese forces. To counter these problems, China requested help from several countries. During the early part of the war, USSR had sent some planes and pilots to assist China. During the Battle of Nanking, a Russian fighter plane was sighted as it was shot down from the sky in an air battle over the city. The Russians withdraw all their forces by summer 1940 when they were having trouble to defend themselves against the Nazi Germans. The next group came to China's aid were the American Flying Tigers. It was a private contractor group run by retired air force officers. Thus, many called them mercenaries. The pilots were receiving $250 per month base salary, plus $500 bounty for each enemy plane shot down. (Note: $750 USD in 1940s = over $11,000 USD in 2012). Their planes were "shark faced". The group claimed the shut down of over 300 Japanese aircraft with only 14 pilots lost.