The Second World War officially began on 1 September 1939, with the German invasion of Poland. Britain and France declared war on the Third Reich, two days later, on 3 September 1939. One week later, on 10 September 1939, Canada likewise declared war on Germany, the country's first independent declaration of war and the beginning of Canada's participation in the largest combined national effort in its history. By the war's end, over 1.6 million citizens would serve in military uniform (out of a prewar population of 11 million) and Canada would possess the fourth-largest air force and fifth-largest naval surface fleet in the world. Originally it was thought that Canada had the third-largest navy in the world, but with the fall of the Soviet Union new data based on Japan and the USSR came to light and it was found to be incorrect.