wmh829386 wrote: ↑Tue Oct 12, 2021 12:01 am
1) It is extremely difficult to compare individual FC system based on operational performance reported by different navies. Especially because RN and USN have difference attitude towards kill counts (I believe you have stress that in previous posts.) Hence it is almost impossible to proof or disproof anything about individual FC system from combat reports. The best could be deduced is only the overall effectiveness with all systems and operational factors combined.
(An analogy would be to attack the Dreyer's Table based on the performance of BCF's shooting... that is another deep deep rabbit hole. But in that case, put a long story short, it was revealed that the BCF gun crews are far below standard during the action. (and even that claim could be controversial) I doubt any individual AA action in WW2 could receive the scrutiny and wealth of gun data like the Jutland does with the added issue of medium & short range AA and CAP in the mix, hence almost nothing could be proven for the LA AA alone.)
2)I can concede that Mk 37/ Mk1 (along with the limited short range AA) was not effective enough to stop the strikes from IJN TB and DB getting through in 1942 and even 1943. But the point is almost moot when FC channels are always saturated in coordinated attacks. It is then justified to claim that a single elaborate LA AA director is far less important than giving multiple short/medium range FC to a ship, which is what was done later. However, it does not mean HACS and Mk37/Mk1 are equally ineffective, and the case of HACS being less effective is quite strong.
3)The problem with the HACS is that the core of the system (HACT deflection screen and assumption of constant height) is not accurate enough to take advantage of radar and VT fuse, while Mk37/Mk1 was quite successful. I can't dig up all the sources (shame!) at the moment but I rely on three main evidences.
1. The report by officers in pre-war exercise that setup that brings burst on target often does not corresponds to observation of target sleeves.
2. Report that VT fuse does not improve performance of DP AA
3. Description of principles of the HACS from the Gunnery Pocket Book
4)The first two are pretty self-evident and Friedman's book on Naval Anti-aircraft gunnery is one place to look for them. The third point need a little bit of explanation and it is quite technical. I should first make a disclaimer; some authors introduced the idea of "tachymetric" FC system and how it is superior, I find that distinction pointless as FC system follows a trend of taking more data and leave less to spotting correction anyway. No mention of that idea will be made.
5)Six numbers are required to represent the velocity and position of a plane. In the case of Mk37/Mk1 it uses bearing from ship, range, height, plane heading, speed, and rate of height change. (Other choices, like in “Flyplane”, are possible) The point is, HACS assumes the rate of height change is zero. And further assumes that the heading of the plane can be approximate by aligning graduation on a telescope to the fuselage, hence ignoring the effect of wind entirely even before ballistic calculation.
6)Multiple issues stem from the approach of HACS. First, if there is wind, the plane heading does not align with the length of its fuselage. Second, if the target is climbing or diving, the fuse timing and the amount of lead will both be wrong. Finally, for diving and climbing targets, because of the assumption and how HACT is integrated, correcting the amount of lead by playing with the speed estimate will just bring the fuse timing off and vice versa, unless the height setting is changed. But the height is calculated from the sight elevation and range finder (radar) to the table, so it cannot be “adjusted” like speed and inclination.
7)With regards to the claim that diving and climbing targets are always accelerating hence cannot be dealt by Mk37/Mk1 system. Although technically true, in the case of Mk37/Mk1, velocity of the target will be updated as the director tracks the target. Even though any solution will be outdated immediately, when compared with the HACS, Mk37/Mk1 will produce a closer firing solution and will be quicker to hit the target when target stop weaving.
8)For the type 285, I should be a bit clearer, it could get height estimate using max signal strength but it is not accurate enough for FC. Mk37 with its radar can lobe switch along vertical axis or horizontal axis, hence it can get accurate elevation, bearing and range on its own, hence can blind fire. Type 285 cannot. To be fair, I am not familiar with the various work-arounds for the HACS. I knew there are eyeshooting sights and GRUB. But I don’t see how they can overcome the inherent problem with the HACT.
9)Going back to the discussion of 4.5" vs 5"/38. The HACS is design to use in salvo fire, hence allowing spotting correction to be applied effectively. Hence the 4.5" with HACS can never develop the same volume of fire as 5"/38 with Mk37/Mk1 even though 4.5" with separate ammunition has similar max RoF.
1)Actually, it's not that difficult if we use postwar analysis by authors such as Lundstrom, Shores and Cull, who carefully compared both sides claims versus actual losses and were able to use the combat reports to assign a probable cause for each aircraft downed. When we do this we can see that RN and USN AA FC performed more alike than not.
2) Post war analysis proves that against level bombers, HACS seems to have performed somewhat better than MK33/37 and even at Midway where the number of IJNAF strikes was small 5in AA was almost a non factor. Lundtrom's assessment was that AA only downed 10 IJNAF aircraft in the carrier TF AA battles at Coral Sea, Midway, and Eastern Solomons versus about 90 award AA kills, and Lundstrom credits the close range AA as getting most of the kills. At Eastern Solomons the USN BuOrd awarded 30 AA kills against 27 IJN strike sorties despite the fact that CAP fighters made numerous kill claims as well. The myth of MK33/37 derived from these these inflated BuOrd AA kill awards, which could not be effectively challenged in wartime and there was no attempt to do so until Lundstrom published his two Volume 'First Team' books on the naval airwar in the Pacific in 1942. OTOH, the RN was far more conservative in awarding AA kills and their wartime assessments were far closer to the truth as Shores and Cull show in their analysis. Unfortunately even authors such as Friedman haven't bother to consult these obvious sources of data, preferring instead to use BuOrd's grossly inflated kill awards.
3) Prewar RN AA drone trials were carefully recorded via phototriangulation and they seem to compare quite well to similar USN drone trials. The RN made it as difficult as possible to bring down target drones and used special low power bursters in their AA shells, and carefully restricted the number of guns per ship allowed to fire at the target, with only one ship allowed to fire on a target at a time.
1) HACS used feedback from observations to continuously correct the FC solution and the addition of radar ranging greatly improved the accuracy of prediction.
2) This isn't correct
3) ?
4) see last sentence of 2 and 3.
5) MK33/37 required the exact same initial inputs as HACS, except they didn't have HACS' optical aids to help them assess target direction. HACS continuously calculated target altitude and used the updated altitude for each FC prediction cycle. Prior to radar MK33/37's range data wasn't sufficiently accurate to allow for introducing target altitude change into the solution and they typically omitted this during target practise. The HADT's CO binocular graticule was used to provide an initial assessment of target course and this was then updated based upon observed target motion to establish a feedback loop and MK33/37 did the same except that they had no optical aid to help calculate the initial inputs. In 1940 the RN began using the Gyro Rate Unit (GRU) and it's computer (GRUB) to provide fully tachymetric data to the HACT and they began to introduce AA FC radars.
6) These issues were common to all AA FC systems. In practise the HACS feedback loop compensated for wind and winds aloft were seldom the same as wind at sea level, so introducing a wind correction was just as likely to harm the FC solution as aid it. Target changes in altitude and range could be predicted by feeding a false altitude and range into the HACT but generally, if the target was changing altitude rapidly it was better to switch to barrage fire aimed by the HADT CO's direct shooting sights. MK33/37 had much the same issues.
7) In practise Mk33/37 couldn't deal with diving targets.
8) MK33/37 didn't begin using MK4 FD radar until mid 1942. There was no inherent reason that HACS couldn't have used FD radar to provide blind fire as it could use all the same data, so this isn't a limitation of HACS, but rather that of the radar provided to it. However, the lighter weight of the HACS HADT and Type 285 radar meant that the weight saved could be used for other purposes such a providing more close range weapons, which ultimately killed the greatest number of aircraft anyways. Basically only low flying torpedo bombers posed a threat to ships at night. RN radar was sufficient to detect if the target was flying low enough to be making a torpedo attack and then radar was used to provide range and bearing (via type 285 lobe switching), with the gun elevation locked at low angles at the probable height of a TB attack. Type 282 radar was used to track AA targets for the close range armament and Type 283 for the main armament, via dedicated AA FC directors and the ABU AA FC computer. Obviously, even at night some aircraft could be detected optically and then the optical angle of sight could be combined with a radar range to provide accurate target height, course, range, bearing and range rate. During daylight targets flying below the HACT elevation limits (about 9 degrees) would be tracked via the eyeshooting sights and the guns fired at precalculated fuze settings for target speed, range and height according to a lookup table.
9) HACS carefully managed deadtime (time between loading the guns and firing them) and added the same DT to the fuze setting for each salvo fired, so that each shell in the salvo had exactly the same fuze setting. This ensured that each salvo produced the maximum lethal effect when the shells burst. OTOH, MK37 had no control over deadtime as the fuze setter ran continuously during the prediction cycle. Thus, as no gun was loaded at the same instant, every shell fired either continuously or via salvo fire, had a different fuze setting and thus the density of each burst pattern was considerably less than for an HACS fired salvo.