Precision Bombing - Second World War

Second World War

See also: Pathfinder force, No. 617 Squadron RAF, and Stabilizing Automatic Bomb Sight

At the start of the Second World War, bombers were expected to strike by daylight to give the best accuracy and to avoid civilian casualties. Cloud cover and industrial haze frequently obscured targets so bomb release was made by dead reckoning from the last navigational "fix" - the bombers dropping their loads according to the ETA for the target. All airforces soon found that daylight bombing resulted in heavy losses since fighter interception became easy and switched to night bombing. This allowed the bombers a better chance of survival, but made it much harder to even find the general area of the target, let alone drop bombs precisely.

The Luftwaffe addressed this issue first by using a series of radio beams to direct aircraft and indicate when to drop bombs. Several different techniques were tried, including Knickebein, X-Gerät and Y-Gerät (Wotan). These provided impressive accuracy - British post-raid analysis showed that the vast majority of the bombs dropped could be placed within 100 yards (91 m) of the midline of the beam, spread along it a few hundred yards around the target point, even in pitch-dark conditions at a range of several hundred miles. But the systems fatally depended on accurate radio reception, and the British invented the first electronic warfare techniques to successfully counter this weapon in the 'Battle of the Beams'

The RAF later developed their own beam guidance techniques, such as GEE and Oboe. These systems could provide an accuracy of about 100yds radius, and were supplemented by the downward-looking radar system H2S. The British development of specialist 'Earthquake' bombs (which needed to be dropped very accurately) led to the development of supporting aiming techniques such as SABS and the Pathfinder Force. Specialist units such as 617 squadron were able to use these and other techniques to achieve remarkable precision, such as the bombing of the Michelin factor at Clermont-Ferrand, where they were required to destroy the workshops but leave the canteen next to them standing.

This development process, driven by the need to bomb in unsighted conditions, meant that by the end of WW2 unguided RAF bombs could be predictably delivered within 25 yards of a target from 15,000 feet height, and precisely on it from low level.

For the US Air Force, daylight bombing was normal based upon box formations for defence from fighters. Bombing was coordinated through a lead aircraft but although still nominally precision bombing (as opposed to the area bombing carried out by RAF Bomber Command) the result of bombing from high level was still spread over an area. The US daytime bombing raids were more effective in reducing German defences by engaging the German Luftwaffe than destruction of the means of aircraft production.

In the summer of 1944, 47 B-29's raided the Yawata steel works from bases in China; only one plane actually hit the target area, and only with one of its bombs. This single 500 lb (230 kg) general purpose bomb represented one quarter of one percent of the 376 bombs dropped over Yawata on that mission. It took 108 B-17 bombers, crewed by 1,080 airmen, dropping 648 bombs to guarantee a 96 percent chance of getting just two hits inside a 400 x 500 ft (150 m) German power-generation plant.