After invading Poland in 1939, Germany next invaded France. The Germans used a new rapid military tactic called "Blitzkrieg" or lightning war in Poland. The USSR and Germany signed a non-aggression pact agreeing not to attack each other. In 1940, over 400,000 British and French soldiers were evacuated from Dunkirk back to Britain. The Battle of Britain primarily involved aircraft. Besides Germany, the USSR also invaded Poland in 1939 according to the terms of the Molotov-Ribbentrop Pact signed by Germany and the USSR.