The RAF 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.[16] Additionally, the Royal Australian Air Force represented around nine percent of all RAF personnel who served in the European and Mediterranean theatres.[17]
In the Battle of Britain in 1940, the RAF defended the skies over Britain against the numerically superior German Luftwaffe.
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 Hitler‘s plans for an invasion of the United Kingdom (Operation Sea Lion). In the House of Commons on 20 August, prompted by the ongoing efforts of the RAF, Prime Minister Winston Churchill eloquently made a speech to the nation, where he said “Never in the field of human conflict was so much owed by so many to so few”.
The largest RAF effort during the war was the strategic bombing campaign against Germany by Bomber Command.
While RAF bombing of Germany began almost immediately upon the outbreak of war, under the leadership of Air Chief Marshal Harris, these attacks became increasingly devastating from 1942 onward as new technology and greater numbers of superior aircraft became available.
The RAF adopted night-time area bombing on German cities such as Hamburg and Dresden, and developed precision bombing techniques for specific operations, such as the “Dambusters” raid by No. 617 Squadron,[19] or the Amiens prison raid known as Operation Jericho.