Blitzkrieg ('lightning war') was the military doctrine used by Germany in the opening stages of World War II.

It involved using fast-moving, concentrated armored divisions (Panzers), supported by close air support, to break through enemy lines and cause panic and dislocation.

The tactic was designed to avoid the static trench warfare of World War I.

After the invasion of Poland, there was a period of inaction on the Western Front known as the 'Phoney War.'

In the spring of 1940, the Blitzkrieg was unleashed on Western Europe.

Germany quickly conquered Denmark, Norway, the Netherlands, and Belgium.

The main German attack on France bypassed the heavily fortified Maginot Line by striking through the Ardennes Forest.

The German Panzers broke through the French lines and raced to the English Channel, encircling the British and French armies.

This led to the dramatic evacuation of over 300,000 Allied soldiers from the beaches of Dunkirk.

France surrendered in June 1940, after only six weeks of fighting, a stunning and unexpected collapse.