In 1940, seven months after the outbreak of World War II, Winston Churchill replaced which person as British prime minister?

At the outbreak of World War II in September 1939, it was Neville Chamberlain who led Great Britain. He was widely known for his pre-war policy of appeasement, famously declaring he had secured "peace for our time" after the 1938 Munich Agreement with Adolf Hitler. However, when Germany invaded Poland, Chamberlain's policy was proven a failure, and he was forced to lead the nation into war.

The initial months of the conflict were known as the "Phoney War," but this period of relative calm ended dramatically in the spring of 1940. The disastrous Allied campaign in Norway, which failed to stop the German invasion there, led to a crisis of confidence in Chamberlain's leadership. A fiery debate in the House of Commons in early May saw his authority crumble as many members of his own party voted against him.

Recognizing he could not command a national unity government, which was seen as essential for the war effort, Chamberlain resigned. His replacement was his First Lord of the Admiralty, Winston Churchill, a long-time critic of appeasement who was seen as the only figure with the energy and resolve to fight the war. In a dramatic turn of events, Churchill officially became prime minister on May 10, 1940, the very same day Germany launched its invasion of France and the Low Countries.