In 1918, the Royal Air Force became the first major independent air force in the world. Formed to serve a strategic need in the most intensive war that Britain had then fought, the RAF continued in the inter-war era to play a key role in the political and diplomatic world, and in defending the Empire. During the Second World War, the RAF was pivotal in defending Britain from invasion in the Battle of Britain, and then in leading the assault on the Axis powers, most notably through the contentious bomber offensive against Germany. In the post-war world, the RAF adapted and developed into a force to meet the needs of the United Kingdom during the Cold War, the retreat from Empire, and most recently in the move to coalition warfare against low intensity threats, all against a backdrop of diminishing resources and shifting priorities. This is the story of the RAF over the first century of its existence: how it has confronted the many challenges and threats it has faced -- from the Luftwaffe in 1940, through the spectre of nuclear holocaust in the Cold War, to the fight against terrorism in the 21st century -- and how it has contributed to the defence of the United Kingdom throughout that period.