27 June 2012
Last updated at 09:05
The aircrews of Bomber Command were volunteers with an average age of 22 who risked their lives flying over occupied Europe. Casualties were high. By 1943 just one in six were expected to survive their first tour.
The chances of getting out of a crashing bomber were slim, and aircraft laden with fuel and bombs were prone to explode instantly when hit by anti-aircraft fire. Bomber Command switched to night raids in an effort to reduce casualties.
The Lancaster and Halifax were the backbone of Bomber Command because of a longer range and greater bomb load than the Stirling or Wellington, which were used on less demanding operations such as laying mines.
Arthur "Bomber" Harris was appointed commander in chief of the unit in February 1942 with a mandate to attack German industry, including sites in the big cities. In May he launched his first "thousand-bomber" raid against Cologne, the scale of which shocked Germany.
Between 300,000 and 600,000 civilians are believed to have died in the bombing of German cities, which were considered legitimate targets as they contained important industrial districts - but navigational technology meant bombing was inaccurate.
The four devastating raids on Dresden in the closing months of the war are among the most controversial operations carried out by Bomber Command. The fire-storms caused by the RAF and US Army Air Force killed about 25,000 civilians and destroyed the city centre.
The Royal Air Force Benevolent Fund says the war could not have been won without the efforts of Bomber Command. It says the attacks forced Germany to divert men, guns and aircraft to defend its airspace, effectively opening a second front long before D-Day.