The Blitz (from German, "lightning") was the period of sustained strategic bombing of the United Kingdom by Nazi Germany during the Second World War.
Between 7 September 1940 and 21 May 1941 there were major aerial raids (attacks in which more than 100 tonnes of high explosives were dropped) on 16 British cities. Over a period of 267 days (almost 37 weeks), London was attacked 71 times, Birmingham, Liverpool and Plymouth eight times, Bristol six, Glasgow five, Southampton four, Portsmouth and Hull three, and there was also at least one large raid on another eight cities. This was a result of a rapid escalation starting on 24 August 1940, when night bombers aiming for RAF airfields drifted off course and accidentally destroyed several London homes, killing civilians, combined with the UK Prime Minister Winston Churchill's immediate response of bombing Berlin on the following night.
Starting on 7 September 1940, London was bombed by the Luftwaffe for 57 consecutive nights. More than one million London houses were destroyed or damaged, and more than 40,000 civilians were killed, almost half of them in London. Ports and industrial centres outside London were also heavily attacked. The major Atlantic sea port of Liverpool was also heavily bombed, causing nearly 4,000 deaths within the Merseyside area during the war. The North Sea port of Hull, a convenient and easily found primary and secondary target for bombers unable to locate their primary targets, was subjected to 86 raids within the city boundaries during the war, with a conservative estimate of 1200 civilians killed and 95% of its housing stock destroyed or damaged. Other ports including Bristol, Cardiff, Portsmouth, Plymouth, Southampton, and Swansea were also targeted, as were the industrial cities of Birmingham, Belfast, Coventry, Glasgow and Manchester. Birmingham and Coventry were heavily targeted because of the Spitfire and tank factories in Birmingham and the many munitions factories in Coventry; the city centre of Coventry was almost completely destroyed.
The bombing did not achieve its intended goals of demoralising the British into surrender or significantly damaging their war economy. The eight months of bombing never seriously hampered British production, and the war industries continued to operate and expand. The Blitz did not facilitate Operation Sea Lion, the planned German invasion of Britain. By May 1941 the threat of an invasion of Britain had passed, and Hitler's attention had turned to Operation Barbarossa in the East. In comparison to the Allied bombing campaign against Germany, the Blitz resulted in relatively few casualties; the British bombing of Hamburg in July 1943 alone inflicted about 42,000 civilian casualties, about the same as the entire Blitz.
Several reasons have been suggested for the failure of the German air offensive. The Luftwaffe High Command (Oberkommando der Luftwaffe, or OKL) failed to develop a coherent long-term strategy for destroying Britain's war industries, frequently switching from bombing one type of industry to another without exerting any sustained pressure on any one of them. Neither was the Luftwaffe equipped to carry out a long-term strategic air campaign, lacking among other things a heavy four-engined bomber, and its intelligence on British industry and capabilities was poor. All of these shortcomings denied the Luftwaffe the ability to make a strategic difference.