The military history of the United Kingdom in World War II covers the Second World War against the Axis powers, starting on 3 September 1939 with the declaration of war by the United Kingdom and France, followed by the UK's Dominions, Crown colonies and protectorates on Nazi Germany in response to the invasion of Poland by Germany. There was little, however, the Anglo-French alliance could do or did do to help Poland. The Phoney War culminated in April 1940 with the German invasion of Denmark and Norway. Winston Churchill became prime minister and head of a coalition government in May 1940. The defeat of other European countries followed – Belgium, the Netherlands, Luxembourg and France – alongside the British Expeditionary Force which led to the Dunkirk evacuation in June 1940.
Almost every country in the world participated in World War II. Most were neutral at the beginning, but only a relative few nations remained neutral to the end. The Second World War pitted two alliances against each other, the Axis powers and the Allied powers. It is estimated that 74 million people died, with estimates ranging from 40 million to 90 million dead. The main Axis powers were Nazi Germany, the Empire of Japan, and the Kingdom of Italy; while the United Kingdom, the United States, the Soviet Union and China were the "Big Four" Allied powers.
Operation Ikarus was a Second World War German plan to invade Iceland, which had been occupied by British forces during Operation Fork in 1940. The plan was never realized.
The history of Canada during World War II 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, Northwestern Europe, 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 a population that as of the 1941 Census had 11,506,655 people, and in forces across the 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.
Naval Air Station Keflavik (NASKEF) is a United States Navy air station at Keflavík International Airport, Iceland, located on the Reykjanes peninsula on the south-west portion of the island. NASKEF was closed on 8 September 2006, and its facilities were taken over by the Icelandic Defence Agency as their primary base until 1 January 2011, when the Agency was abolished and the base handed over to the Icelandic Coast Guard, which has operated the base until 2017. US forces returned to Keflavik in 2016, renovating parts of the base to accommodate P-8As on short duration/expeditionary detachments.
The military history of the United States during World War II covers the nation's role as one of the major Allies in their victory over the Axis Powers. The United States is generally considered to have entered the conflict with the 7 December 1941 surprise attack on Pearl Harbor by the Empire of Japan and exited it with the 2 September 1945 surrender of Japan. During the first two years of World War II, the US maintained formal neutrality, which was officially announced in the Quarantine Speech delivered by US President Franklin D. Roosevelt in 1937. While officially neutral, the US supplied Britain, the Soviet Union, and China with war materiel through the Lend-Lease Act signed into law on 11 March 1941, and deployed the US military to replace the British forces stationed in Iceland. Following the 4 September 1941 Greer incident involving a German submarine, Roosevelt publicly confirmed a "shoot on sight" order on 11 September, effectively declaring naval war on Germany and Italy in the Battle of the Atlantic. In the Pacific Theater, there was unofficial early US combat activity such as the Flying Tigers.
The Northrop N-3PB Nomad was a single-engined American floatplane of the 1940s. Northrop developed the N-3PB as an export model based on the earlier Northrop A-17 design. A total of 24 were purchased by Norway, but were not delivered until after the Fall of Norway during the Second World War. Exiled Norwegian forces used them from 1941, operating from Iceland, for convoy escort, anti-submarine patrols, and training purposes from "Little Norway" in Canada. Within two years of delivery, the design was obsolete for front-line service and the remaining N-3PBs were replaced by larger aircraft in 1943.
The Royal Norwegian Navy Air Service was alongside the Norwegian Army Air Service the forerunner to the modern-day Royal Norwegian Air Force.
Plan W, during World War II, was a plan of joint military operations between the governments of Ireland and the United Kingdom devised between 1940 and 1942, to be executed in the event of an invasion of Ireland by Nazi Germany.
The Allied leaders of World War II listed below comprise the important political and military figures who fought for or supported the Allies during World War II. Engaged in total war, they had to adapt to new types of modern warfare, on the military, psychological and economic fronts.
The Kingdom of Iceland was a sovereign and independent country under a constitutional and hereditary monarchy that was established by the Act of Union with Denmark signed on 1 December 1918. It lasted until 17 June 1944 when a national referendum established the republic of Iceland in its place.
The British invasion of Iceland by the United Kingdom's Royal Navy and Royal Marines occurred on 10 May 1940, during World War II. The invasion took place because the British government feared that Iceland would be used militarily by Nazi Germany, which had overrun Denmark a month earlier. Although Iceland was independently governed, it was in a personal union with Denmark, which was largely responsible for its foreign relations. The Government of Iceland issued a protest, charging that its neutrality had been "flagrantly violated" and "its independence infringed".
At the beginning of World War II, Iceland was a sovereign kingdom in personal union with Denmark, with King Christian X as head of state. Iceland officially remained neutral throughout World War II. However, the British invaded Iceland on 10 May 1940. On 7 July 1941, the defence of Iceland was transferred from Britain to the United States, which was still a neutral country until five months later. On 17 June 1944, Iceland dissolved its union with Denmark and the Danish monarchy and declared itself a republic, which it remains to this day.
When the United Kingdom declared war on Nazi Germany in September 1939 at the start of World War II, it controlled to varying degrees numerous crown colonies, protectorates, and India. It also maintained strong political ties to four of the five independent Dominions—Australia, Canada, South Africa, and New Zealand—as co-members of the British Commonwealth. In 1939 the British Empire and the Commonwealth together comprised a global power, with direct or de facto political and economic control of 25% of the world's population, and of 30% of its land mass.
The North Atlantic air ferry route was a series of Air Routes over the North Atlantic Ocean on which aircraft were ferried from the United States and Canada to Great Britain during World War II to support combat operations in the European Theatre of Operations (ETO).
Iceland Base Command (IBC) is an inactive United States Army organization. It was established for the United States defense of the Kingdom of Iceland during World War II. It was inactivated on 4 March 1947.
Royal Air Force Kaldadarnes or more simply RAF Kaldadarnes is a former Royal Air Force station at Kaldaðarnes, near the town of Selfoss, Iceland.
Operation Pilgrim was a planned British operation to invade and occupy the Canary Islands during World War II. The invasion was a contingency plan to be executed in the event of a known plan whereby Germany would support Spain in occupying Gibraltar, the Azores, the Canary Islands as well as the Cape Verde Islands. The British feared that such occupation would materially affect Allied access to the Mediterranean and endanger Britain’s shipping-lanes to its Dominions. Operation Pilgrim was a preemptive invasion and occupation to prevent German control of the islands. The German invasion never materialised and consequently, Operation Pilgrim was never put into action.
Air transport in Iceland is the transportation of cargo and passengers within Iceland, and internationally between Iceland and the rest of the world.
United Kingdom 
Canada 
United States 
Kingdom of Iceland (until 1944)
Republic of Iceland (from 1944)
