"C" Force was the Canadian military contingent involved in the Battle of Hong Kong in December 1941. Members of this force were the first Canadian soldiers to see action against Japan in World War II. The major Canadian units involved in the defence of Hong Kong were the Winnipeg Grenadiers and the Royal Rifles of Canada. In addition to this the Canadians provided a Brigade HQ.

During the course of 1941, Japan's foreign policy assumed an increasingly aggressive posture towards the Western powers. In July 1941, Japan occupied the southern half of French Indochina, leading the United States, Great Britain, and the Dutch government in exile which controlled the oil-rich Netherlands East Indies (modern Indonesia) to impose an oil embargo on Japan. As Japan possessed no oil, the embargo threatened to shut down the Japanese economy once its oil reserves were exhausted. Talks were opened to find a solution to the crisis, but it was understood that there was a very real possibility that Japan might try to seize the Netherlands East Indies together with the British colonies of Sarawak, Sabah, Malaya, and Burma to provide itself with oil, as proven by the subsequent occupations of the Japanese Army. The British response was a policy of "deterrence diplomacy", building up British forces in Asia to deter the Japanese from choosing war and to encourage Tokyo to continue seeking a diplomatic solution to the crisis. As part of the same strategy, Force Z, a force consisting of one battleship, one battlecruiser, and three destroyers, was ordered to Singapore to provide a deterrent. A major problem with the British "deterrence diplomacy" was that in 1941, Britain was fully engaged in war with Germany and Italy, and it was not possible to build up the level of forces in Asia that could truly deter the Japanese. In a memo, Major-General A. E. Grasett (the outgoing Commander of British Troops in China, and a Canadian himself) argued that increasing the size of the Hong Kong garrison would have "a strong psychological stimulus" and a "salutary effect on the Japanese". Grasett's memo stated that an extra two battalions could be "found" in Canada, though he also noted that any "troops supplied by Canada would be practically untrained". However, since the purpose of the Canadian troops in Hong Kong would be to deter the Japanese, not actually fight them, Grasett argued that this would not matter. Grasett's memo was endorsed by the Foreign Secretary, Anthony Eden. In a memo to the Prime Minister Winston Churchill, on 12 September 1941, Eden called Japan an overrated power that would back down if confronted with sufficient British power and approved of sending two Canadian battalions to Hong Kong as the best way to "keep up the pressure". As Churchill had stated he would only make the request to the Canadian government if Eden gave his approval first, Eden's statement that he and the other Foreign Office experts all believed that Japan would be less likely to choose war if faced with a stronger Hong Kong garrison was decisive in winning his support.

Ever since the Sino-Japanese war began in 1937, Britain had leaned towards pro-Chinese neutrality, assisting China under the belief that it was better to keep Japan bogged down in China to ensure that Japan did not attack the Dominions of Australia and New Zealand, along with Britain's Asian colonies. The British historian Victor Rothwell wrote: "In the middle 1930s, if China had a Western friend, it was Britain. In 1935–36 Britain gave China real help with its finances and showed real concern about Japanese encroachments in north China. Realizing that the only hope of inducing Japan to moderate these activities lay in an Anglo-American joint front, Britain proposed that a number of times, but was always rebuffed by Washington". From time to time, the Chinese leader Chiang Kai-shek hinted that he might be willing to make peace with Japan. Given the crisis caused by the oil embargo, the Foreign Office in London felt it was imperative to keep China fighting and viewed reinforcing the Hong Kong garrison as a symbol of support for China. As the British Army was fully involved in the campaigns in North Africa and the Horn of Africa, a request was made on 19 September 1941 to have Canada provide two battalions to Hong Kong. The British request of 19 September stated that "there have been signs of a certain weakening of Japan's attitude towards us" and argued that sending two battalions to Hong Kong would "have a very strong moral effect on the whole of the Far East".

In Ottawa, the Department of National Defence had neither a map of Hong Kong nor any accurate information to provide the basis for decisions. The Minister of National Defence, Colonel John Ralston, was visiting the United States at the time of the request, and the acting Defence Minister was Major Charles "Chubby" Power. Power had won the Military Cross in World War One, but the primary reason for his appointment as associate defense minister was because of his influence and popularity in his native Quebec. Power was an affable and bilingual Irish-Canadian from Quebec City whose Catholicism, skill as a hockey player, and sympathy for French-Canadian sentiments had established him as a leading spokesman for Quebec. Hence his appointment as associate defense minister, even though, as the Canadian historian Brereton Greenhous noted sourly, Power was not known for "the keenness of his intellect". The Canadian prime minister, William Lyon Mackenzie King, privately considered Power to be a mental lightweight and kept him in the cabinet only because he was very popular in Quebec. In turn, Power consulted General Harry Crerar, the Chief of the General Staff, who favored approving the request. Many of the officers in the Royal Rifles of Canada regiment were relatives or friends of the Power clan of Quebec City, and Power's own son Francis was serving as a subaltern in the Royal Rifles. In 1940–1941, the Royal Rifles had served in the British colony of Newfoundland, charged with protecting it against the unlikely prospect of a German invasion. For many officers in the Royal Rifles, being transferred from guarding the cold, fog-shrouded shores of Newfoundland to guarding the warm, tropical city of Hong Kong was a highly pleasing prospect. The Royal Rifles were tasked with guarding the Newfoundland Railway and the Gander airport, both of which were considered unglamorous duties. In September 1941, Major J.H. Price, the son of a Quebec lumber baron who was serving in the Royal Rifles, wrote to Power saying, "With the interest you have in our welfare, you will be willing and able to convince military authorities that it is bad policy to keep a unit like ours killing time". Power, in his reply to Price, stated that he "made inquiries" about sending the Royal Rifles overseas and now had "some hope that events overseas may soon develop to the point where it is possible for your lot to have the opportunity it deserves".

The matter was first discussed at the Cabinet on 23 September 1941, with Power advocating for acceptance of the request. Mackenzie King agreed, provided that Ralston also gave his approval. Ralston was still in the United States and, from his hotel in Los Angeles, telephoned Crerar for his advice and learned that he still favored acceptance. Crerar then submitted a memo to the cabinet stating his professional opinion as a soldier, asserting that there was "no military risk" to sending a force to Hong Kong, as he optimistically concluded that sending two battalions to Hong Kong would deter Japan from war.

Largely for domestic political reasons, the Liberal Mackenzie King accepted the request on 29 September 1941. In 1917, the issue of conscription caused the Liberal Party to split between its English-Canadian wing, which supported conscription, and its French-Canadian wing, which opposed conscription. In 1917, the Canadian Corps had taken such heavy losses that the government of Robert Borden had the stark choice of either pulling the Canadian Corps out of action, which was tantamount to dropping out of the war, or bringing in conscription to provide sufficient manpower to keep the Canadian Corps fighting. By opting for the second option, it led to the Conscription Crisis of 1917, which posed the gravest threat to national unity yet seen, as the policy of conscription led to the first demands that Quebec secede from Canada. Mackenzie King was determined that in the Second World War, his Liberal Party would not be likewise broken into two by the conscription issue as it had been in 1917. Mackenzie King seems to have genuinely believed that if his government followed the same policies that Borden had in 1917-18, it would cause a civil war. To avoid dealing with the issue of conscription, Mackenzie King tried to keep the Canadian Army from seeing action, reasoning that if the Army fought no battles, it would take no losses, and thus there would be no need for conscription. For much of the Second World War, King preferred to limit Canada's contributions to the war to the struggle in the air and on the sea as the best way to avoid the level of casualties that would lead to demands for overseas conscription. By 1941, the fact that after two years of war, the Canadian Army had not seen action once, while the armies of the other nations of the "Commonwealth family" had all seen extensive action, leading to domestic criticism of Mackenzie King. By September 1941, many English-Canadian politicians and journalists were starting to display signs of jealousy as soldiers from Britain, Australia, and New Zealand got all the glory of fighting the Axis forces in the Mediterranean while the Canadians sat on the sidelines in Britain, leading to demands that Mackenzie King dispatch Canadian troops to Egypt, which he stoutly resisted. Mackenzie King's adamant refusal to send the Canadian Army into action by 1941 was hurting morale, as many soldiers complained that it was the airmen of the Royal Canadian Air Force who were getting all the glory while they were forced to engage in endless training for battles that the prime minister would not allow them to fight. By the fall of 1941, Mackenzie King's nemesis, Arthur Meighen, was campaigning for the leadership of the Conservative Party on a platform of "Total War", accusing Mackenzie King of being lackluster in his commitment towards winning the war.

Mackenzie King agreed to send C Force to Hong Kong because it allowed him to claim that his government was supporting Britain. At the same time, since the purpose of C Force was to deter the Japanese from invading Hong Kong, it seemed to promise there would be no losses in combat. Crerar's memo, claiming that there was "no military risk," had considerable influence on Mackenzie King, who believed that C Force would only be performing guard duty in Hong Kong. Additionally, the assertion that C Force would deter Japan from going to war enabled Mackenzie King to assert that Canada was playing an important role in protecting the British Empire, which helped him resist the pressure to send Canadian troops to fight in Egypt. Mackenzie King appears to have either been unaware or did not care that Crerar, a bureaucratic general who had never seen action, had an "authoritarian submissive" personality and tended to say whatever his superiors wanted to hear.

In autumn 1941, the British government accepted the Canadian government's offer, mediated by Major-General Grasett, a former general officer commanding in Hong Kong and Canadian, to send two infantry battalions (1,975 personnel) to reinforce the Hong Kong garrison. At that time, war with Japan was not considered imminent, and it was expected that these battalions would see only garrison (non-combat) duty. The Canadian Army's classification of units was divided into three classes, with Class A at the top and Class C at the bottom. The two battalions selected by Crerar were both Class C units, evaluated at the lowest level of fitness for combat. The first unit chosen by Crerar was the Royal Rifles of Canada, selected primarily because of lobbying by Associate Defence Minister Power, who insisted that the Royal Rifles, full of his relatives and friends, go to Hong Kong. Mackenzie King's diary mentions in passing in December 1941 that "it was Power himself who was keenest on having the Quebec regiment [the Royal Rifles] go, he mentioning at the time that his own son was a member of it."