Of all the ‘practice’ wars that preceded the main events of the second world war, including the Spanish civil war and the winter war between Finland and the Soviet Union, the least well known is the four-month war on the Mongolia-Manchurian border between the Soviet Union and Japan that ended in September 1939.

This is not surprising, perhaps, because British attention was (and still is) more focused on Hitler’s invasion of Poland that took place two weeks earlier.