The history of Canada during the Second World War begins with the German invasion of Poland on 1 September 1939. While the Canadian Armed Forces were eventually active in nearly every theatre of war, most combat was centred in Italy,Canadian War Museum "The Italian Campaign" . Retrieved on: 5 August 2007. Northwestern Europe,Canadian War Museum "Liberating Northwest Europe" . Retrieved on: 5 August 2007. and the North Atlantic. In all, some 1.1 million Canadians served in the Canadian Army, Royal Canadian Navy, Royal Canadian Air Force, out of 11,506,655 Canadians (1941 Census). Canadians served in forces across the British Empire, with approximately 42,000 killed and another 55,000 wounded. During the war, Canada was subject to direct attack in the Battle of the St. Lawrence, and in the shelling of a lighthouse at Estevan Point on Vancouver Island, British Columbia.

The financial cost was $21.8 billion between 1939 and 1950. By the end of the war Canada had the world's fourth largest air force,Canadian Air Force Journal, Vol. 3, No. 1, "World's Fourth Largest Air Force?" and third largest navy.World War – Willmott, H.P. et al.; Dorling Kindersley Limited, London, 2004, Page 168 Retrieved on: 17 May 2010. The Canadian Merchant Navy completed over 25,000 voyages across the Atlantic,Veterans Affairs Canada "The Historic Contribution of Canada's Merchant Navy" . Retrieved on: 5 August 2007. 130,000 Allied pilots were trained in Canada in the British Commonwealth Air Training Plan. On D-Day, 6 June 1944 the 3rd Canadian Infantry Division landed on "Juno" beach in Normandy, in conjunction with allied forces. Canada contributed to the Manhattan Project via Montreal Laboratory. The Second World War had significant cultural, political and economic effects on Canada, including the conscription crisis in 1944 which affected unity between francophones and anglophones. The war effort strengthened the Canadian economy and furthered Canada's global position.Stacey, C. "World War II: Cost and Significance". The Canadian Encyclopedia online (Historica). Revised by N. Hillmer. Retrieved on: 5 August 2007.

Preparations Though Canada was the oldest Dominion in the British Empire, it was, for the most part, reluctant to enter the war. Canada, with a population somewhere between 11 and 12 million at the time, eventually raised very substantial armed forces for the war. Around 10% of the entire population of Canada joined the army, with only a small portion being conscripted. After the long struggle of the Great Depression of the 1930s, the challenges of the Second World War accelerated Canada's ongoing transformation into a modern urban and industrialized nation.

Canada informally followed the British Ten Year Rule, which reduced defence spending even after Britain abandoned it in 1932. Having suffered from nearly 20 years of neglect, Canada's armed forces were small, poorly equipped, and mostly unprepared for war in 1939. King's government began increasing spending in 1936, but the increase was unpopular. The government had to describe it as primarily for defending Canada, with an overseas war "a secondary responsibility of this country, though possibly one requiring much greater ultimate effort." The Sudeten crisis of 1938 caused annual spending to almost double. Nonetheless, in March 1939 the Permanent Active Militia (or Permanent Force (PF), Canada's full-time army) had only 4,169 officers and men while the Non-Permanent Active Militia (Canada's reserve force) numbered 51,418 at the end of 1938, mostly armed with weapons from 1918. In March 1939 the Royal Canadian Navy had 309 officers and 2967 naval ratings, and the Royal Canadian Air Force had 360 officers and 2797 airmen.

Under Secretary of State for External Affairs Oscar D. Skelton stated the government's war policy. Among its highlights: Consult with Britain and France, and "equally important, discreet consultation with Washington." Prioritize Canadian defence, especially the Pacific coast. Possibly aid Newfoundland and the West Indies. The RCAF should be the first to serve overseas. Canada can "most effective[ly]" serve its allies by providing munitions, raw materials, and food.

King's cabinet approved this policy on 24 August 1939, and in September disapproved of the proposal by the Chiefs of Staff to create two army divisions for overseas service, in part because of cost. His "moderate" war strategy soon demonstrated its national and bilingual support in two elections. When Premier of Quebec Maurice Duplessis called an election on an antiwar platform, Adélard Godbout's Liberals won a majority on 26 October 1939. When the Legislative Assembly of Ontario passed a resolution criticizing the government for not fighting the war "in the vigorous manner the people of Canada desire to see," King dissolved the federal parliament, and at the resulting election on 26 March 1940, his Liberals won the largest majority in history.

Outbreak of war Declaration of war

When the United Kingdom declared war on Germany in August 1914, Canada was a Dominion of the British Empire with full control over only domestic affairs and thus automatically joined the First World War. After the war, the Canadian government wanted to avoid a repeat of the Conscription Crisis of 1917, which had divided the country and French and English Canadians. Stating that "Parliament will decide," Prime Minister William Lyon Mackenzie King avoided participating in the Chanak Crisis in 1922, partly since the Parliament of Canada was not in session.

The 1931 Statute of Westminster gave Canada autonomy in foreign policy. When Britain entered World War II in September 1939, some experts suggested that Canada was still bound by Britain's declaration of war because it had been made in the name of their common monarch, but Prime Minister King again said that "Parliament will decide."

In 1936, King had told Parliament, "Our country is being drawn into international situations to a degree that I myself think is alarming." Both the government and the public remained reluctant to participate in a European war, partly because of the Conscription Crisis of 1917. Both King and Opposition Leader Robert James Manion stated their opposition to conscripting troops for overseas service in March 1939. Nonetheless, King had not changed his view of 1923 that Canada would participate in a war by the Empire whether or not the United States did. By August 1939 his cabinet, including French Canadians, was united for war in a way that it probably would not have been during the Munich Crisis, although both cabinet members and the country based their support in part on expecting that Canada's participation would be "limited."

It had been clear that Canada would elect to participate in the war before the invasion of Poland on 1 September 1939. Four days after the United Kingdom had declared war on 3 September 1939, Parliament was called in special session and both King and Manion stated their support for Canada following Britain, but did not declare war immediately, partly to show that Canada was joining out of her own initiative and was not obligated to go to war. Unlike 1914 when war came as a surprise, the government had prepared various measures for price controls, rationing, and censorship, and the War Measures Act of 1914 was re-invoked. After two days of debate, the House of Commons approved an Address in Reply to the Speech from the Throne on 9 September 1939 giving authority to declare war to King's government. A small group of Quebec legislators attempted to amend the bill, and CCF party leader J. S. Woodsworth stated that some of his party opposed it. Woodsworth was the only Member of Parliament to vote against the bill.James Shaver Woodsworth, Canadian Encyclopedia. Retrieved 29 March 2016Once Upon a Time, Canadians could be proud of Parliament, Globe and Mail, May 04, 2012. Retrieved 29 March 2016 The Senate also passed the bill that day. The Cabinet drafted a proclamation of war that night, which Governor General Lord Tweedsmuir signed on 10 September. King George VI approved Canada's declaration of war with Germany on 10 Sept..Donald Creighton, The Forked Road: Canada 1939-1957, McClelland and Stewart, 1976, p.2. Canada later also declared war on Italy (11 June 1940), Japan (7 December 1941), and other Axis powers, enshrining the principle that the Statute of Westminster conferred those sovereign powers on Canada.

Mobilization and deployment

At the outbreak of war, Canada's commitment to the war in Europe was limited by the government to one division, and one division in reserve for home defence. Nevertheless, the eventual size of the Canadian armed forces greatly exceeded those envisioned in the pre-war period's so-called mobilization "schemes." Over the course of the war, the army enlisted 730,000; the air force 260,000; and the navy 115,000 personnel. In addition, thousands of Canadians served in the Royal Air Force. Approximately half of Canada's army and three quarters of its air force personnel never left the country, compared to the overseas deployment of approximately three-quarters of the forces of Australia, New Zealand, and the United States. By war's end, however, 1.1 million men and women had served in uniform for Canada. The navy grew from only a few ships in 1939 to over 400 ships, including three aircraft carriers and two cruisers. That maritime effort helped keep the shipping lanes open across the Atlantic throughout the war.

In part, this reflected Mackenzie King's policy of "limited liability" and the labour requirements of Canada's industrial war effort, but it also reflected the objective circumstances of the war. With France defeated and occupied, there was no Second World War equivalent of the First World War's Western Front until the invasion of Normandy occurred in June 1944. While Canada sent 348 troops, the manpower requirements of the North Africa and Mediterranean theatres were comparatively small and readily met by British and other British Empire/Commonwealth forces.

While the response to war was initially intended to be limited, resources were mobilized quickly. Convoy HX 1 departed Halifax just six days after the nation declared war, escorted by and . The 1st Canadian Infantry Division arrived in Britain on 1 January 1940.Byers, p. 26 By 13 June 1940, the 1st Battalion of The Hastings and Prince Edward Regiment was deployed to France in an attempt to secure the southern flank of the British Expeditionary Force in Belgium. By the time the battalion arrived, the British and allies were cut off at Dunkirk, Paris had fallen, and after penetrating 200 km inland, the battalion returned to Brest and then to Britain.

Apart from the Dieppe Raid in August 1942, the frustrated Canadian Army fought no significant engagement in the European theatre of operations until the invasion of Sicily in the summer of 1943. With the Sicily Campaign, the Canadians had the opportunity to enter combat and later were among the first to enter Rome.

Canada was the only country of the Americas to be actively involved in the war prior to the attack on Pearl Harbor.

Canadian support for the war was mobilized through a propaganda campaign, including If Day, a staged Nazi invasion of Winnipeg that generated more than $3 million in war bonds.

Early campaigns

Although it regularly consulted with Canada, Britain was essentially in charge of both countries' war plans during the first nine months of the war. Neither nation seriously planned for Canada's own defence; Canada's training, production, and equipment emphasized combat in Europe. Its primary role was to supply food, raw materials, and to train pilots from throughout the Empire with the British Commonwealth Air Training Plan the British proposed on 26 September 1939, not send hundreds of thousands of troops overseas as it had done in World War I.