During World War II, the Trans-Siberian Railway played an important role in the supply of the powers fighting in Europe. In 1939, the USSR signed a non-aggression pact with Germany. While Germany's merchant shipping was interdicted by the Western allies, the Trans-Siberian Railway (along with its Trans-Manchurian branch) served as the essential link between Germany and Japan. One commodity particularly essential for the German war effort was natural rubber, which Japan was able to source from South-East Asia (in particular, French Indochina).