Military history of the United Kingdom during World War II

The military history of the United Kingdom in World War II covers the Second World War against the Axis powers. On 3 September 1939, the British government declared war on Nazi Germany in response to the invasion of Poland. France declared war later the same day. Further declarations of war followed from the UK's Dominions, Crown colonies and protectorates. 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.

Britain and its Empire continued the war against Germany. Churchill engaged industry, scientists and engineers to advise and support the government and the military in the prosecution of the war effort. Germany's planned invasion of the UK was averted by the Royal Air Force denying the Luftwaffe air superiority in the Battle of Britain, and by its marked inferiority in naval power. Subsequently, urban areas in Britain suffered heavy bombing during the Blitz in late 1940 and early 1941. The Royal Navy sought to blockade Germany and protect merchant ships in the Battle of the Atlantic. The Army counter-attacked in the Mediterranean and Middle East, including the North-African and East-African campaigns, and in the Balkans.

The United Kingdom and allied countries signed the Declaration of St James's Palace in June 1941 committing to no separate peace with Germany and setting out principles to serve as the basis of a future peace. Churchill agreed an alliance with the Soviet Union in July and began sending supplies to the USSR. By August, Churchill and American President Franklin Roosevelt had drafted the Atlantic Charter to define goals for the post-war world. In December, the Empire of Japan attacked British and American holdings with near-simultaneous offensives against Southeast Asia and the Central Pacific including an attack on the US fleet at Pearl Harbor. Britain and America declared war on Japan, opening the Pacific War. The Grand Alliance of the United Kingdom, the United States and the Soviet Union was formed and Britain and America agreed a Europe first grand strategy for the war. The Declaration by United Nations drafted by Roosevelt and Churchill in Washington in December 1941 formalised the Allies of World War II. The UK, the US and their Allies suffered many disastrous defeats in the Asia-Pacific war during the first six months of 1942. The Eastern Front between the Soviet Union and Nazi Germany became the largest theatre of war ever to take place.

There were eventual hard-fought victories in 1943 in the North-African campaign, led by General Bernard Montgomery, and in the subsequent Italian campaign. British forces played major roles in the production of Ultra signals intelligence, the strategic bombing of Germany, and the Normandy landings of June 1944. The liberation of Europe followed on 8 May 1945, achieved by the Soviet Union, the United States, the United Kingdom and other Allied countries. The Battle of the Atlantic was the longest continuous military campaign of the War.

The Pacific War, fought primarily between China, the United States and Japan, was geographically the largest theater of the war. In the South-East Asian theatre, the British Eastern Fleet conducted strikes in the Indian Ocean. The British Army led the Burma campaign to drive Japan out of the British colony; involving a million troops at its peak, drawn primarily from British India, the campaign was finally successful in mid-1945. The British Pacific Fleet took part in the Battle of Okinawa and the final naval strikes on Japan. British scientists contributed to the Manhattan Project to design a nuclear weapon. The decision to use these weapons was made by the Anglo-American Combined Policy Committee and led to the surrender of Japan, which was announced on 15 August 1945 and signed on 2 September 1945.

For the domestic history see British home front during World War II.

Background

Although the UK had increased military spending and funding prior to 1939 in response to the increasing strength of Germany under the Nazi Party, its forces were still weak by comparison, especially the British Army. Only the Royal Navy – at the time still the largest in the world"Royal Navy in 1939 and 1945". Naval-history.net. 8/7/11 – was of a greater strength than its German counterpart. The British Army only had nine divisions available for war, whereas Germany had seventy-eight and France eighty-six.N.H. Gibbs, Grand Strategy: Volume 1 Rearmament Policy History of the Second World War (1976) HMSO

Nonetheless, Britain was "a very wealthy country, formidable in arms, ruthless in pursuit of its interests and sitting at the heart of a global production system from its empire."; After becoming prime minister in 1940, Winston Churchill engaged industry, scientists and engineers to advise and support the government and the military in the prosecution of the war effort. Much of the scientific work that led to technology that determined the outcome of the war, such as radar, was done before 1940, and shared with the Americans that year through the Tizard Mission, which led to extensive Allied technological cooperation. Several technologies invented in Britain proved critical to the military and were widely manufactured by the Allies during the Second World War.Paul Kennedy, Engineers of Victory: The Problem Solvers Who Turned The Tide in the Second World War (2013)James W. Brennan, "The Proximity Fuze: Whose Brainchild?," U.S. Naval Institute Proceedings (1968) 94#9 pp 72–78.

Nuclear weapons research began during the war, in 1941, with the UK's Tube Alloys project, which was absorbed into the American Manhattan Project, to which British scientists contributed.; see book review by Under the clause of the 1943 Quebec Agreement that specified that nuclear weapons would not be used against another country without mutual consent, the atomic bombing of Japan was recorded as a decision of the Combined Policy Committee.

Beginning of the conflict Anticipating a German attack, the Polish Navy implemented the Peking Plan in late August and early September 1939, moving three modern destroyers, , , and to Britain; the ships served alongside (and under the command of) the Royal Navy for the remainder of the war.

On 3 September, the UK and France declared war on Germany as obliged by the Anglo-Polish military alliance. The declaration was made 24 hours after the UK had issued an ultimatum to Germany to withdraw all German forces from Poland. After the fall of Poland, the Royal Navy was strengthened by the arrival of two Polish submarines and . The Polish Navy in the United Kingdom was then supplemented with leased British ships.

The British Army immediately began dispatching the British Expeditionary Force (BEF) to support France. At first only regular troops from the pre-war Army made up its numbers. In 1940, however, men of the Territorial Army (TA) divisions being mobilized in the UK were sent. In the end, the BEF had I, II and III Corps under its command, controlling 200,000 men. The Royal Air Force (RAF) also sent significant forces to France at the start of hostilities. Some were French Army cooperation squadrons to help with matters like reconnaissance for the French Army. Others were Hawker Hurricane squadrons from RAF Fighter Command. Separately, Bomber Command sent the Advanced Air Striking Force, composed of squadrons flying the Fairey Battle and other machines that did not have the range to reach Germany from the UK.J.R.M. Butler, Grand Strategy: Sept. 1939 – June 1941 (1957)pp 151–74

During the Phoney War, the RAF carried out small bombing raids and a large number of propaganda leaflet raids (code-named "Nickels") and the Royal Navy imposed a coastal blockade on Germany.

The British army began the war with a paper force of 900,000 men 232,000 active regulars, 185,000 regular reserves, 34,000 in the militia, 428,000 in the territorial army and 21,000 in the territorial army reserve however of the many non active regular formations a total manpower amount of 480,000 was available in September 1939 thus the actual force was 700,000 and this figure includes those who were in training or filling non-combat roles at the outbreak of hostilities.

Western and northern Europe, 1940 and 1941

Norwegian campaign

Norway loomed large in German strategy because of the great iron ore deposits in northern Sweden and the long seacoast that would preclude a blockade of the sort that hurt Germany in the First World War. Predicting correctly that the UK would make a preemptive move against neutral Norway to stop the flow of ore from Narvik, Adolf Hitler ordered an invasion to begin on 9 April 1940. The Wehrmacht succeeded in their mission, landing a large force at vital strategic points in Norway. British land forces were quickly sent to Norway, landing in the centre at Åndalsnes and at Namsos and in the north of the country at Narvik. The Luftwaffe deterred landings farther south.J.R.M. Butler, Grand Strategy: Sept. 1939 – June 1941 (1957) pp 119–50

British troops made amphibious landings at Namsos during April 1940 in an effort to stop the Germans advancing North. The British Forces' attacks south were stopped and they were soon surrounded in the town of Namsos. The British were faced with attacks from the Luftwaffe and increasing difficulty with landing fresh troops and supplies from the sea.Steinkjer Encyclopedia: Bombing Sunday General De Wiart was given orders to evacuate his forces on 28 April. All British troops were evacuated by 4 May 1940.

In central Norway, Royal Navy aircraft-carriers and RAF fighter squadrons could not keep the established bases secure, and the British had to evacuate them. In the north, the Germans were driven out of Narvik after they had captured it. However, as Luftwaffe aircraft came into range with the German advances, it was again found to be impossible to sustain bases in the face of aerial threat. British forces in Narvik were withdrawn as well.François Kersaudy, Norway 1940 (1998)

As a consequence of the loss of Norway and Denmark, the Royal Navy commenced a pre-emptive occupation of the Faroe Islands on 12 April 1940.

On 10 May 1940, the Royal Navy occupied Iceland to install naval and air bases on this Atlantic island.Donald F. Bittner, The Lion and the White Falcon: Britain and Iceland in the World War II Era (1983)

The Battle of France

Following the German invasion of Poland on 1 September 1939, the British Expeditionary Force was sent to the Franco-Belgian border in mid-September. The first deployment was completed by 11 October 1939 at which point 158,000 men had been transported to France. Over the next few months, troops, materials and vehicles continued to arrive in France and Belgium and by 13 March 1940 the BEF had doubled in size to 316,000 men.

This period leading up to 10 May 1940 was known as the Phoney War, as there was little combat apart from minor clashes of reconnaissance patrols. The Allied generals believed that time was on their side, and hoped to weaken Germany by blockade before going on the offensive.Thomas B. Buell, John N. Bradley, John H. Bradley, The Second World War: Europe and the Mediterranean Square One Publishers 2002, (pp.43-44)