Bomb Weights Contreversy
One of the obvious difficulties in sinking a U-boat was getting the D.C. on target. There were two main types of error in aiming namely range and line errors. Range error is when the centre of the stick is either behind or in front of the centre of the U-boat. Line error is when the line of the stick does not pass through the centre of the U-boat. By looking at the accounts of pilots based on the number of times they claim to have hit their target the aiming error was estimated to be 20 yards in range and 10 in line. However by looking at the damage done to U-boats in these attacks the success rate was much lower than expected given the size of the explosions. This gave an estimate of the aiming error of around 60 yards in range and 25 in line. These two points of view are clearly opposite.
They could only be reconciled if either the pilots were not as accurate as they claimed or the bombs were less powerful than first thought. The Admiralty pushed the idea that the bombs needed to be made larger. They pushed for a 600lb bomb. This would increase the lethal radius and therefore improve the success rate. The O.R.S however argued that this was not the best way as only modest improvements in the lethal radius could be found. They suggested switching to a 100lb bomb and having the bombers drop more at a time. This did not go down well with the Admiralty as they found the idea that if the bombs are too small for the job even smaller ones could be used difficult to accept. The O.R.S also argued that it was likely pilots were over estimating their accuracy. There was therefore a push for greater evidence of the accuracy. This was done by using photographic evidence.
The early method of photographing an attack was by the use of handheld cameras. This was very easy to organise however the results were not very useful. This is because unless there is some sort of fixed reference point the distance between the aircraft and explosion cannot be determined accurately. The solution was to have a fixed camera which would take a series of photographs during an attack. These photographs would then need to be altered as the angle of the camera meant that scale was not uniform. This was first done by reprojecting the photograph. This involved projecting the photograph with a lens of the same focal length as the original camera. The tilt of the picture can then be altered to make the horizon horizontal giving a true scale photograph. The scale can then be calculated if the height is known but since this was not usually the case, scale was estimated by looking at other references such as the U-boat or explosion plumes.
