Before World War II began, there was a general acceptance that the strategic bombing of cities and industrial areas would be a major factor in deciding the outcome of any future war. In 1932, British Prime Minister Stanley Baldwin gave a speech in which he noted that “the bomber will always get through.”
This phrase became widely quoted in the pre-war years among those who believed in the effectiveness of strategic bombing. It was claimed that fleets of well-armed bombers would be able to accurately deliver their loads to targets deep within enemy territory. When the war began in September 1939, it rapidly became clear that this was not so.
Daylight raids by British bombers, mainly against German naval bases, led to such high losses that they were quickly discontinued. Daylight operations by the aircraft of Bomber Command were limited throughout the remainder of 1939, and by the spring of 1940 most bombing raids were being carried out at night.
This switch to night bombing reduced the losses experienced during daylight operations, but it also inevitably meant that bombing accuracy was decreased. Nevertheless, the Royal Air Force (RAF) was confident that it was effectively striking its targets.
The British bombing campaign continued into 1941 with increasing numbers and sizes of raids using twin-engine bombers such as the Wellington, Hampton, and Whitley, as well as the first of the four-engine British bombers, the Short Stirling.
The RAF claimed that the bulk of its bombs were falling on their targets. For example, in the weekly Cabinet briefing for July 17-24, 1941, it was noted that attacks had been carried out on industrial and rail targets in Frankfurt, Mannheim, Cologne and Hanover.
The Cabinet were told that “Over 670 tons of H.E. and over 58,000 incendiary bombs were dropped, and it is estimated that a large proportion of these fell in the target areas.”
The RAF was confident that it was inflicting serious damage on the Nazi capacity for industrial production, but not everyone agreed. One of those was Professor A. V. Hill, a noted British scientist who was also a Member of Parliament.
Hill gave a speech to Parliament in which he pointed out that German bombing of British cities in 1940 had actually led to an increase in civilian morale and had not significantly reduced British industrial capacity: “The loss of production in the worst month of the Blitz was about equal to that due to the Easter holidays.”
Hill questioned whether the British bombing of German industrial capacity was really as effective as the RAF was claiming.
One of Prime Minister Winston Churchill’s most trusted advisors, physicist Frederick Lindemann, 1st Viscount Cherwell, agreed and he persuaded Churchill to commission an independent report on the effectiveness of British night bombing.
The task of compiling the report was given to one of Lindemann’s assistants, a young economist working for the Statistical Section of the Admiralty, David Bensusan-Butt.
Butt analyzed photographs of over one hundred separate raids by RAF night-bombers which had taken place in June/July 1941—the same period covered by the Cabinet briefing paper quoted above in which the RAF claimed that “a large proportion”of its bombs were hitting their targets. These photographs covered forty-eight targets and over five hundred individual sorties.
The report was completed and published in August 1941 and its contents were both shocking and devastating. Of bombers which reported that they had successfully bombed, on average, only one in five had actually dropped their bombs within five miles of the target. For targets in the heavily defended Ruhr, this dropped to one in ten. On nights when there was a new moon, this fell to one in fifteen.
And this included only aircraft which claimed to have successfully bombed the target—it did not cover those which for a variety of reasons had not been able to complete their mission. Butt went on to note:
It must be observed also that by defining the target area for the purpose of this enquiry as having a radius of five miles, an area of over 75 square miles is taken. This must at least for any town but Berlin consist very largely of open country. The proportion of aircraft actually dropping their bombs on built up areas must be very much less.
For all the courage, professionalism and determination of the British bombers crews, it was clear that most of their bombs were falling harmlessly on open country and very, very few were actually hitting the factories and rail-yards which were their targets.
It was estimated that only 1% of all bombs dropped actually fell in the immediate vicinity of their target. Far from delivering a decisive blow to German industry, the RAF was losing crews and aircraft for almost no discernible effect.
A heated debate followed in which detractors of the RAF sought to divert resources to other parts of the British armed forces. Instead, the RAF continued its night bombing campaign, but switched from “precision bombing” to “area bombing.”
In February 1942, the Area Bombing Directive was issued. This switched RAF attacks from industrial and transportation targets, which the Butt report showed that they were incapable of hitting reliably, to attacks on whole German cities in order to directly disrupt the German industrial workforce and undermine the morale of the German population.
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As the war progressed, the RAF’s capacity to hit targets at night increased dramatically. The Pathfinder Force, highly trained bomber crews equipped with the latest navigation devices, began operations in 1942, dropping flares to guide the rest of the bomber fleet to their target.
Radio navigation devices including Oboe, GEE and G-H became widely fitted to new British bombers such as the Halifax and Lancaster in 1942/1943. In early 1943 the first airborne, ground-scanning radar, H2S, was fitted to some RAF bombers, allowing them to identify and accurately bomb targets even in clouds and haze.
By the end of WWII, RAF bombers were able to reliably drop bombs within twenty-five yards of their target from 15,000 feet. When RAF bombers of 617 Squadron attacked the Michelin tire factory at Clermont-Ferrand in France in March 1944, they were able to minimize French casualties by completely destroying the vital workshops while leaving the canteen alongside largely undamaged.
The publication of the Butt report in 1941 was a painful shock, not just to the RAF but to the entire British government. However, instead of leading to the abandonment of the night-bombing campaign, it instead provided vital impetus in the drive to improve British bombing accuracy.