The Royal Air Force (RAF) is the United Kingdom's air and space force. It was formed towards the end of the First World War on 1 April 1918, becoming the first independent air force in the world, by regrouping the Royal Flying Corps (RFC) and the Royal Naval Air Service (RNAS). Following the Allied victory over the Central Powers in 1918, the RAF emerged as the largest air force in the world at the time. Since its formation, the RAF has taken a significant role in British military history. In particular, it played a large part in the Second World War where it fought its most famous campaign, the Battle of Britain.The RAF's mission is to support the objectives of the British Ministry of Defence (MOD), which are to "provide the capabilities needed to ensure the security and defence of the United Kingdom and overseas territories, including against terrorism; to support the Government's foreign policy objectives particularly in promoting international peace and security". The RAF describes its mission statement as "... [to provide] an agile, adaptable and capable Air Force that, person for person, is second to none, and that makes a decisive air power contribution in support of the UK Defence Mission". The mission statement is supported by the RAF's definition of air power, which guides its strategy. Air power is defined as "the ability to project power from the air and space to influence the behaviour of people or the course of events".Today, the Royal Air Force maintains an operational fleet of various types of aircraft, described by the RAF as being "leading-edge" in terms of technology. This largely consists of fixed-wing aircraft, including those in the following roles: fighter and strike, airborne early warning and control, intelligence, surveillance, target acquisition, and reconnaissance (ISTAR), signals intelligence (SIGINT), maritime patrol, air-to-air refuelling (AAR) and strategic & tactical transport. The majority of the RAF's rotary-wing aircraft form part of the tri-service Joint Helicopter Command in support of ground forces. Most of the RAF's aircraft and personnel are based in the UK, with many others serving on global operations (principally over Iraq and Syria) or at long-established overseas bases (Ascension Island, Cyprus, Gibraltar, and the Falkland Islands). Although the RAF is the principal British air power arm, the Royal Navy's Fleet Air Arm and the British Army's Army Air Corps also operate armed aircraft.