British were not the first to make use of heavier-than-air military aircraft, the RAF is the world's oldest independent air force: that is, the first air force to become independent of army or navy control. The RAF was founded on 1 April 1918 (during World War I) by the amalgamation of the Royal Flying Corps (RFC) and the Royal Naval Air Service (RNAS), as recommended in a report prepared by Jan Smuts. At that time it was the largest air force in the world. Its headquarters was located in the former Hotel Cecil. After the war, the RAF was drastically cut and its inter-war years were relatively quiet. The RAF was put in charge of British military activity in Iraq, and carried out minor activities in other parts of the British Empire, including establishing bases to protect Singapore and Malaya. The RAF's naval aviation branch, the Fleet Air Arm, was founded in 1924 but handed over to Admiralty control on 24 May 1939. The RAF adopted the doctrine of strategic bombing, which led to the construction of long-range bombers and became its main bombing strategy in the Second World War. Second World War The Royal Air Force underwent rapid expansion prior to and during the Second World War. Under the British Commonwealth Air Training Plan of December 1939, the air forces of British Commonwealth countries trained and formed "Article XV squadrons" for service with RAF formations. Many individual personnel from these countries, and exiles from occupied Europe, also served with RAF squadrons. By the end of the war the Royal Canadian Air Force had contributed more than 30 squadrons to serve in RAF formations, similarly, approximately a quarter of Bomber Command's personnel were Canadian. Additionally, the Royal Australian Air Force represented around nine percent of all RAF personnel who served in the European and Mediterranean theatres. During the Battle of Britain in 1940, the RAF defended the skies over Britain against the numerically superior German . In what is perhaps the most prolonged and complicated air campaign in history, the Battle of Britain contributed significantly to the delay and subsequent indefinite postponement of Operation Sea Lion, Hitler's plans for an invasion of the UK. In the House of Commons on 20 August, prompted by the ongoing efforts of the RAF, Prime Minister Winston Churchill made a speech to the nation, where he said "Never in the field of human conflict