The so-called phoney war was the period of the Second World War between the fall of Poland in October 1939 and the German invasion of Denmark and Norway in April 1940. Having failed to prevent the defeat of Poland in September 1939, Britain and France expected to wage a long and exhausting war with Germany, but there followed over six months of stagnation and stalemate in western Europe.
There was some action at sea, notably the Battle of the River Plate and the attack on Scapa Flow by the submarine U-47 under Kapitänleutnant Günther Prien. Britain lost HMS Royal Oak at Scapa Flow and Germany lost KMS Admiral Graf Spee at the River Plate. Even so, little happened on land or in the air. Some brief skirmishes apart, both sides remained behind their defences and concentrated on building up their forces. Britain and France prioritised a naval blockade of Germany. The situation was labelled both the "phoney war" and as a play on words, blitzkrieg ("lightning war") became sitzkrieg ("sitting down war").
At home, Britain implemented its civil defence plans immediately to be prepared for German bombing raids. Air raid precautions were rigorously imposed and, in nearly all aspects of their daily lives, people had to comply with government regulations and restrictions. These included conscription and food rationing.
The "phoney war" ended in the spring of 1940 when Germany went on the offensive. They invaded Denmark and Norway on 9 April and then, on 10 May, the same day that Winston Churchill became Prime Minister, they invaded Belgium and the Netherlands to end the stalemate in western Europe.