The difference is really that some seem to think that with the SABS sight hitting a battleship, even stationary, was a simple thing. The SABS sight was not some miraculous instrument, in fact at the same time as 617 Sqn was achieving an average radial error of 170 yards (later improved to 125 yards), 9 Sqn was achieving an error of 195 yards with the Mk XIV sight. The difference was just 25 yards, not as great as some imagine.
I think that hitting a stationary battleship was a remarkable achievement, even given the better sight, and was the result of much time on the practice range. The Tirpitz attackers may have been operating in an era of allied air superiority but they still flew at an altitude above some of the more deadly forms of flak. The higher you fly the less accurately you bomb. The 8th AF considered this one of the most successful aspects of German flak defences.
Anybody know how many large warships, with the exception of Tirpitz, were hit by level bombers flying at 15,000 ft or above in all theatres during WW2?
Cheers
Steve
The distribution of bombs for a typical CEP (circular area probable) is approximately as follows.
A/ within one radius of the CEP 50%
B/ outside of one radius but within two 43%
C/ outside two radii 7%
Within one radius of the CEP the distribution of bombs in terms of area is approximately even though there is a some clustering towards the centre.
The distribution is Rayleigh (two dimensional Gaussian) ie the normal curve. Form a statistical mathematical point of view it would have been nicer for the CEP to be defined as the radius which contains 63% of hits. I've seen that the Germans at least defined the accuracy of their FLAK radars in this way.
Accuracy degrades as per a cube law though I've heard it claimed that the probability of a hit in naval artillery is according to a power of 5 law. I am not convinced, I can see how a square law applies to ballistic fall of an side ways deviation of a projectile which accelerates and thus integrates according to a square law.
Hence a 10% increase in bombing altitude would increase CEP by 33% or 50% depending on which law you believe is the truth and apply.
The Lancasters that attacked the Tirpitz bombed from between 12500ft and 16000ft. The former is likely what achieved the hits.
If we assume 617 squadron achieved 170yards/150meter CEP at 17000ft they would achieve significantly better at 16000ft and dramatically better at 12000ft.
But take the example of 32 bombs with a CEP of 170yard/150meters, 617's assumed CEP at 17000ft, and noting that each 50% reduction in radius would have 25% of the bombs.
A 16 bombs would be within 150m
B 4 bombs within 75m
C 1 bomb within 37.5m. Suggesting a high probability of a hit, greater than 50%, since the radius with an area equal to Tirpitz was around 45m.
These radii could be reduced about 6.5% for 16000ft as compared to 17000ft.
Using the cube law bombing at 12500ft as opposed to 17000ft should double accuracy but using a conservative linear approximation reduce CEP 12500ft/17000ft x 170yards = 125yards/112meters.
Lets run our calculation again, for 32 bombs dropped from 12500ft with a CEP of 112 meters.
A/ 16 bombs would fall within 112 meters
B/ 4 bombs would fall within 56 meters
C/ 1 bomb would fall within 27 meters, the Tirpitz can be assumed to have an area with a radius of 45 meters on the basis of its area.
If we consider the slight clustering effect and that the improvement between 17000ft and 12500ft was probably due to a cube law then the odds look quite good.
It's worth noting that the raid was a repeat of another 32 bomber raid conducted in October 1944 in the same fjord so in effect about 60 bombs were dropped.
*************
Early bombsights simply were set at an angle according to tables and didn't use optics but use a tongue and V similar to a traditional rifle, the RAF initially preferred this for night use. They contained elementary mechanical elements to help the course to be set in the presence of estimated wind etc. If the aircraft was jostled or its angle of attack varied then the bombsight could go off by a few degrees that could equal hundreds of meters.
The first major improvement in bombsights seems to have been the introduction of gyroscopically stabilised optics. Quite oddly it seems the RAF tried a computing bombsight without a gyroscopically levelled platform in the ABS I and so did the Luftwaffe with the Lotfe 7A, it would seem pointless to carry out accurate calculations from such an unstable datum. Once stabilised, using a pendulum that was averaged out by gyroscopes there was a stable datum.
The difference between the Mk.14 bombsight and the SABS IIB was that the Mk.14 simply told the bomb aimer/pilot where the bombs were going to land, even in a slight dive and while manoeuvring, the sight also helped the bomb aimer set a course to run over the target. The wind drift or estimated target motion had to be estimated and manually entered so it was no good against a moving ship if bomb fall time was a factor or stiff winds. Meteorological aircraft and master bombers probably provided this information.
The SABS IIB was similar to the Norden and Lotfe 7. It added a function in which the ground or targets relative motion could be tracked. Effectively a mechanism (tachograph ?) tracked a fixed spot on the ground on the basis of altitude of the aircraft and target as well as the aircrafts true air speed.
The bombardier then adjusted some variable speed drives and this adjustment is in fact the wind drift (or in the case of a moving ship its velocity vector). The sight now put out actual ground speed and the magnitude of the cross, head wind.
We know the bomb trail, we know how long it will take to hit the 'ground' and it is now possible to come up with an aiming solution.
Navies had been doing it for decades (Dreyer tables, the more advanced Pollen system) and it had been done in FLAK predictors.
As far as attacking a ship is concerned it would make little difference if it was stationary or moving to a wind correct bombsight. So long as it moved in a straight line as merchant ships did.