British military history of World War II

This article is about the military history of the United Kingdom during World War II. The United Kingdom, along with most of its Dominions, Crown colonies, and British India, declared war on Nazi Germany in September 1939, after the German invasion of Poland. War with Japan began in December 1941, after it attacked British colonies in Asia. The Axis powers were defeated by the Allies in 1945.

Although the UK had increased military spending and funding prior to 1939 in response to the increasing strength of Nazi Germany (Germany under the Nazi Party ), its forces were still weak by comparison, especially the British Army. Only the Royal Navy – at the time the largest in the world – was of a greater strength than its German counterpart. The British Army only had nine divisions available for war, whereas Germany had 78 and France 86.

Anticipating the outbreak of the Second World War, the Polish Navy implemented the Peking Plan in late August and early September 1939, moving three modern destroyers, Burza (Storm), Błyskawica (Lightning), and Grom (Thunder) 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 Orzeł (Eagle) and Wilk (Wolf). The Polish Navy in the United Kingdom was then supplemented with leased British ships.

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