When World War II began in 1939, Canada debated whether to join the war before ultimately voting to support the Allied effort under Prime Minister King. While not as enthusiastic as in WWI due to the horrors remembered and economic struggles, Canadians volunteered in large numbers. Canada's major contribution was the British Commonwealth Air Training Plan, which saw 130,000 pilots trained in Canada. The government also took a "total war" approach to fully mobilize the economy. Key battles included the British evacuation at Dunkirk and the Battle of Britain, which halted Hitler's plans to invade the UK. Japan's bombing of Pearl Harbor drew the US into the war against Germany and Italy in Europe and Japan in the Pacific.