British 4.5"/45 (11.4 cm) vs American 5"/38 (12.7 cm) Mark 12

[dunmunro]

1) Of course radar is a definite advantage, but it does not change the the problem with HACS using fictitious speed and heading to correct for the ballistic effect of wind and the inability for HACT to feedback the change of height to the sights means that the feedback system used in HACS are often ineffective. The need to use fictitious input while controlling with GRU just further illustrates the point: even though wind at altitude cannot be measured, a ballistic correction should not interfere with the tracking data in the FC system.

2)It seems to me very difficult to justify HACS is equal or superior to Mk37/Mk1. You may argue that HACS Mk IV with Type 285 is better than Mk37 with optical RF. But that's just illustrates how revolutionary radar was.

3)For the examples of engagement, I am not sure how comparable is it between kills of land based twin engine bomber and naval based single engine bomber. The number of planes and organization of the attack can post various degree of challenge to the AA batteries. The problem is further compound by the effectiveness target distribution and weather. In the case of the success from HMS Scylla, the attacking planes were designated to the director long before effective gun range and maintain height and course in a single large group. It's not hard to imagine that MK37/Mk1 with radar would perform even better at similar engagements.

I was in the process of typing a lengthy reply when it all vanished.

1) This a minor issue and seems not to have been a problem for HMS Ulster Queen or Scylla.

2) In 1942 Mk 37 performed very poorly. This is just a fact, as I have shown, and easily understood by reading Lundstrom. The RN was using the systems that it started the war with in 1939 and certainly could not have waited until 1943 for a debugged Mk 37, aided by VT ammo to have appeared. The USN had the luxury of an additional two years of peace to work on Mk37 and still couldn't get it to work well until VT ammo saved the day for it:

The post-war (USN) Pacific Fleet lessons-learned board asserted that Mk 37 and other heavy gun fire
control systems were inefficient against fast manoeuvring aircraft such as Kamikazes. ‘The
introduction of the VT fuse was a shot in the arm to the basic system which enabled it to stagger
through the war by partially concealing its inherent weakness...’ (Friedman)

However lets pretend, that by magic, the RN had introduced Mk37 in 1938. A Mk 37 DCT weighs a minimum of 12.5 tons versus ~3.5 tons for the combined HA/LA directors on a Tribal/JK class destroyer or 5.5 tons for a MK4 GB director a cruiser or KGV class battleship. For a Tribal/JK Class each ton of DCT weight = ~5 tons of upper deck weight (March, British Destroyers). So a Tribal/JK class destroyer would have had to shed over 40 tons of weight at the upper deck level which would have led to surrendering at least one twin 4.7in mount and the quad pom-pom. For USN pre-Fletcher class destroyers it meant surrendering a 5in mount and/or most of the torpedoes and restricting the close range AA to 4 or 6 .5in MGs. Yet even in 1942 it was a woefully inefficient AA FC system.

Lundstrom estimated that USN AA shot down these numbers of aircraft during the carrier actions at:

Coral Sea = 3
Midway = 3 (all but one of Yorktown's destroyer screen had Mk37)
Eastern Solomons = 4.
Santa Cruz = 25

Yet the RN AA shot down as many aircraft during defending PQ18 as in all four of the USN's 1942 carrier battles! This is from the CO of the destroyers defending Yorktown:

5. Of the estimated four Jap planes which reached the carrier, three were observed shot down during retirement: one by own VF, one by Balch short range weapon fire (1.1 and 20 MM battery), and one by Balch 5" battery firing a 2.0 second barrage using A.A. common projectile fitted with the Mark XVIII time fuze...

CONCLUSIONS AND RECOMMENDATIONS AS A RESULT OF THE ACTION.

(a) The 5" battery and close range weapons of surface ships are only partially effective in repelling a determined torpedo attack because of the low rate of fire of the 5" battery and fuze failures; short effective range of the 20 MM guns; and the failure of short range weapon gunners to lead the target sufficiently.
http://www.ibiblio.org/hyperwar/USN/rep ... sRon6.html

The only 5in AA kill observed was from Balch's guns in Barrage fire (Balch had low angle 5in and NO 5in AA FC!) and one from her augmented CIWS, which she could carry since she wasn't crippled by the weight of a Mk 37 DCT!

3) The USN enjoyed good weather for most of their engagements. Luftwaffe aircraft were faster, armoured and had self sealing fuel tanks, and were harder to bring down than the IJNAF aircraft which lacked these features.

[wmh829386]

1), 2) Those problem are certainly minor if you only look at accounts of successful engagements! It is easy to name quite a few engagements where the RN AA was not successful, say Battle of Crete, the East India raid, Operation Pedestal, and Force Z where AA fire is not enough to prevent lost of important fleet unit. Does that proof HACS performed very poorly and it's just a fact?

However I do mostly agree that it is impossible for RN to develop something like the Mk37 in time given the time and resources constraint. However, the consideration doesn't make HACS the better system in terms of performance. I am curious about the weight argument though, what are the sources for the weight of the various directors?

Finally, about PQ 18. The comparison is not fair. The number of size and ships in the Convoy is much larger than any TF in the early Pacific carrier battles. And the strikes stretched over much longer time because of the weather and nature of convoy actions. The strikes in CV battles comes in much shorter time with higher coordination and far more fighters to take the kills.

3) Again, the coordination of strikes, attack profile, efficiency of early warning all contributes to the number of planes shoot down. Even when weather is fine, the fighter direction and target designation of the USN in the early war was not good while IJN strikes are well coordinated. Finally, Single engine bombers are smaller targets and These factors make AA less effective and more kills will go to the fighters. Furthermore many have mentioned how little Mk37 was available at 1942, it is not wise to use the performance in 1942 to judge the FC system.

[dunmunro]

(1) 1), 2) Those problem are certainly minor if you only look at accounts of successful engagements! It is easy to name quite a few engagements where the RN AA was not successful, say Battle of Crete, the East India raid, Operation Pedestal, and Force Z where AA fire is not enough to prevent lost of important fleet unit. Does that proof HACS performed very poorly and it's just a fact?

2)However I do mostly agree that it is impossible for RN to develop something like the Mk37 in time given the time and resources constraint. However, the consideration doesn't make HACS the better system in terms of performance. I am curious about the weight argument though, what are the sources for the weight of the various directors?

3)Finally, about PQ 18. The comparison is not fair. The number of size and ships in the Convoy is much larger than any TF in the early Pacific carrier battles. And the strikes stretched over much longer time because of the weather and nature of convoy actions. The strikes in CV battles comes in much shorter time with higher coordination and far more fighters to take the kills.

4) Again, the coordination of strikes, attack profile, efficiency of early warning all contributes to the number of planes shoot down. Even when weather is fine, the fighter direction and target designation of the USN in the early war was not good while IJN strikes are well coordinated. Finally, Single engine bombers are smaller targets and These factors make AA less effective and more kills will go to the fighters. Furthermore many have mentioned how little Mk37 was available at 1942, it is not wise to use the performance in 1942 to judge the FC system.

1) Yes, they are minor because other factors such as range accuracy, fuze timing, time of flight, etc, are far more important.

AA was what it was. Shores and Cull analysed the air-sea Battle of Crete and their conclusion was that RN AA shot down about 15 Luftwaffe aircraft (The RN claimed 22 according to Cunningham's despatch written in June 1941) with the majority of the kills falling to the massed RN AA on 21 May. This certainly was a defeat, but we have a fleet, with almost no fighter cover, under constant air attack from nearby bases and the major losses occurred amongst detached forces that ultimately ran out of ammo before succumbing to air attack. Again analysis by Shores shows about 15-18 AA kills over Pedestal. However, compare the AA kill totals to the USN's results in the PTO in 1942; only 10 USN AA kills in their first 3 carrier TF versus air attacks and the USN had the benefit of massed and concentrated AA around the intended targets (their carriers). The USN's dismal AA results against level bombers at Bougainville (Feb 1942) is another case in point. During the Ceylon raids isolated RN ships, with no aircover, were quickly overwhelmed by massed dive-bombers. Force Z shot down 4 IJN aircraft - yes, a poor result but compare it to USN AA at Bougainville. The IJN official history stated:

Prince of Wales was desperately unlucky in being crippled so early in the action, and neither Captain Leach nor his crew had much chance to show what they were worth after that. Her 5.25-in. guns were a menace to the Japanese aircraft to the end, and their Official History pays this tribute:

"The anti-aircraft fire of the British ships was extremely fierce and the damage suffered by the aircraft bombing from a straight and level approach at high altitude was very great. Consider just the Takeda squadron of eight aircraft which bombed last, when Prince of Wales had already reduced speed to about 6 knots and was sinking. Five of Takeda’s aircraft were hit. *"

This damage was caused by just two turrets, S1 and S2; how effectively might the full complement of these guns have performed had they not been
robbed of power and denied a level platform by the early damage and the resulting list of Prince of Wales. (Middlebrook and Mahoney, Battleship)

2) The problem is that the historical record simply doesn't demonstrate that MK37 was superior in combat prior to the introduction of VT ammo. I have looked at this very carefully.

3) C'mon. Compare PQ18 to Santa Cruz. The USN was able to mass their AA firepower around their carriers whilst, in comparison, the RN had to spread their AA escorts over a vast area and could never develop the intensity of fire that the USN could. Yes, comparisons are not always straightforward but a feature in almost all the RN convoy battles was the necessity to spread the screen around a slow moving convoy, rather than around a ~30 knot carrier.

4) IJN aircraft were far more vulnerable than the faster, well armoured Luftwaffe strike aircraft that also had self sealing fuel tanks (think about that). The IJN strikes were not well coordinated and if they were it would have been curtains for the USN carriers in almost every action. This is were you really need to read Lundstrom carefully. USN fighter cover also forced the IJNAF to hurry their attacks, whilst at Crete, for example, Luftwaffe aircraft could circle their targets and strike almost at their leisure. I pointed out that MK37 was present in numbers at Midway, Eastern Solomons and Santa Cruz and I think, I proved that it was ineffective at Santa Cruz and Midway and the low kill count shows that it was ineffective at Eastern Solomons as well. This is really the crux of the problem; the historical record shows Mk37 was ineffective during prewar trials and it shows that it was ineffective during all of 1942. The problem is that BuOrd falsified the kill totals, grossly overstating them, for Mk37 and then published the faked data and we've all been dealing with the consequences of this ever since. BuOrd awarded almost 400 AA kills in the Pacific in 1942, when the actual number was about 60, and the vast majority of these were via the close range AA and even amongst the 5in kills many were accomplished during barrage fire, or in local control and in both cases the FC computer was cut out of the fire control system.

There was a debate in the RN about AA fire control, before, during and after, WW2. Under normal historical circumstances there would have been a sober analysis of AA efficacy and a careful comparison of RN and foreign AA technology and AA results... But this didn't happen because BuOrd faked their data and thus fatally poisoned any possibility of an accurate and fair analysis. It's only since Lundstrom that we can actually look at the reality of the situation versus the fantastical story told by the USN's BuOrd.

BuOrd's 'official bag' of awarded AA kills in 1942:

http://www.sfu.ca/~dmunro/images/USN_AA ... ims_42.pdf

See the 4th page where BuOrd claims that the above numbers are UNDERESTIMATED by 50%!!!!

[dunmunro]

1) Of course radar is a definite advantage, but it does not change the the problem with HACS using fictitious speed and heading to correct for the ballistic effect of wind and the inability for HACT to feedback the change of height to the sights means that the feedback system used in HACS are often ineffective. The need to use fictitious input while controlling with GRU just further illustrates the point: even though wind at altitude cannot be measured, a ballistic correction should not interfere with the tracking data in the FC system.

Just to address this. Friedman was describing the operational use of the HACS1 HACT (in 1930!) where defects in the deflection screen exaggerated the problem. The introduction of HACS III and it's HACT III (1935) corrected most of these defects and by 1939 most, if not all, the earlier HACTs had been replaced and/or rebuilt to HACT III specifications. From the HACS III manual:

THE HIGH ANGLE CONTROL SYSTEMS, MARKS III AND IIIC
The High Angle Control System Mark III is fundamentally the same as the H.A.C.S. Marks I*** and II***, the main difference being the use of an improved transmission system consisting of oil power motors with A.B.C. control in place of electrical D.C. motors. The design of the calculating table has been altered to improve the accessibility of parts and the general maintenance.

2. The most important modifications introduced in the Mark III system may be summarised as follows. Some of these have since been or are being incorporated in the Mark I and Mark II tables. ...

(c) Range/height conversion gear has been completely re-designed to
overcome the mechanical faults of H.A.C.S. I and to give increased
accuracy. ...

(i) Target speeds up to 350 knots can be set, and an improved projection
system is fitted, the latter being considerably more accurate than H.A.C.S. I. Certain projection inaccuracies inherent in previous types of projection units have been to a great extent obviated by moving the position of the axis of the tilting plate relative to the axis of
projection. (1) The provision of a gyro roll corrector in place of the liquid pendulum
type for feeding roll into the table. This corrector is a separate unit and also provides power stabilisation of the director sight in the vertical sight plane (roll compensation) in the Mark III* director...

[Byron Angel]

d

Meanwhile, here is a first-hand eye-witness account of HACS versus Mk37 from an American source for your consideration -
The author was Admiral Ed Hooper, then Fire Control Officer (later Gunnery Officer) aboard USS Washington in WW2. The passage is extracted from his 1964 reminiscences (on file at the US Navy Dept Historical Section) of the summer of 1942 when USS Washington was part of a USN task force operating with the British Home Fleet to cover the Murmansk convoys –

“One day, shortly after leaving the Scapa Flow channel, the Home Fleet was ordered to battle stations. As planes towing sleeves circled the column of battleships and cruisers, Commander Home Fleet would designate a ship to fire. British heavy caliber antiaircraft fire was fantastically poor. USS Tuscaloosa’s fire was close, Wichita’s highly accurate, ours tore the sleeve immediately to shreds. The performance was repeated during subsequent runs.

Our next operation found us flooded by top officers and civilians from the Admiralty. Our antiaircraft gunnery was a primary reason ...”

The only time that DoY and Washington exercised AA fire together was:

From: 1200 April 6, 1942 to 1200 April 7, 1948.
(a) Moored in Scapa Flow.

(b) HMS Renown and USS WASP stood out. Commander-in-Chief, Home
Fleet, made official call on Comtaskfor 39. At 1113 underway in
company with DUKE OF YORK and six destroyers for gunnery practice.
OTC Vice-Admiral in DUKE OF YORK,. Steamed at various courses and
speeds in Flow operating area.

From: 1200 April 7, 1942 to 1200 April 8, 1942.

(a) Fired 80 rounds of 5"/38 anti-aircraft ammunition, AATP-S,
port and starboard batteries, at sleeve towed by British plane.
fired 1"1, 20mm, and .50 cal. machine gun batteries at sleeve.

DUKE OF YORK fired secondary battery at same sleeve. Total
ammunition fired: 806 rounds .50 cal., 514 rounds 20mm, 185
rounds 1"1. Starboard paravane line carried away. Recovered
paravane. Fired 48 rounds 5"/38 cal. at surface target, Day
Spotting Practice, following DUKE OF YORK on each run. Held
main battery tracking exercise on KENT. RAF Spitfires made
simulated attack to train lookouts, target designators, and
secondary battery. Held instruction of officers and mount cap-
tains of anti-aircraft battery in plane identification, using
British films of British and German planes. Moored to Buoy "E",
Scapa Flow, at 2114. Morning of 8th HMS VICTORIOUS stood in and
anchored. WICHITA and TUSCALOOSA stood out for gunnery practices.

(BB56 War diary)

So Hooper's memory was faulty as per the dates and the presence of WICHITA and TUSCALOOSA. No mention of the sleeve being shot down.

- - -

dunmunro,
You are far too conveniently selective, evasive and disingenuous in your responses; they constitute very unfortunate obstructions to any sort of honest and rational discussion.

Nothing you excerpted from the BB56 war diary whatsoever disputes Hooper's account in any way whatsoever. Read Musicant's operational history of USS Washington (which draws upon official USN operational and historical archives as well as numerous personal accounts of serving officers and crew. USS Washington arrived at Scapa Flow in the first week of April 42, but remained in the Scapa/Hvalfjord/Arctic Ocean are of operations through the PQ17 Murmansk run. Washington did not depart until mid-July 1942. Hooper was aboard her for the entire period - Apr-Jul 42. I'm guessing that you yourself have never seen, let alone read, Hooper's documents and reminiscences which officially reside in USN archives.

Why do you continue to wave Lundstrom around when you have the original USN AA analyses available? Have you bothered to distinguish between RN AA kills achieved by LAA and MAA (neither of which had anything to do with HACS or FKC) versus those actually effected by HACS/FKC controlled heavy AA? Have you bothered to read the HACS analyses by Pugh, Peat, Porteous or Marland? Have you bothered to compare the RPB figures for HACS/FKC versus contemporary Mk37 figures?

Are you aware that the US refused to release any of their VT fuze production for British HACS/FKC-equipped ships because evaluations had indicated that the effectively unstabilized HACS directors then in service were unable to reliably deliver fire within VT fuzing radius. GRUDOU was a sufficient stop-gap solution, but was only put to paper at the end of 1942, prototype-tested in early 1943, and not fully fitted in the fleet until the end of 1944. VT ammunition was provided only to those ships with HACS directors fitted with GRUDOU stabilization. You could read about this in more detail than I am presenting if you had a copy of "From Fellside to Flyplane", but the self-publishing author sadly passed away in June of this year and the book is no longer available.


Byron

[dunmunro]

d

Meanwhile, here is a first-hand eye-witness account of HACS versus Mk37 from an American source for your consideration -
The author was Admiral Ed Hooper, then Fire Control Officer (later Gunnery Officer) aboard USS Washington in WW2. The passage is extracted from his 1964 reminiscences (on file at the US Navy Dept Historical Section) of the summer of 1942 when USS Washington was part of a USN task force operating with the British Home Fleet to cover the Murmansk convoys –

“One day, shortly after leaving the Scapa Flow channel, the Home Fleet was ordered to battle stations. As planes towing sleeves circled the column of battleships and cruisers, Commander Home Fleet would designate a ship to fire. British heavy caliber antiaircraft fire was fantastically poor. USS Tuscaloosa’s fire was close, Wichita’s highly accurate, ours tore the sleeve immediately to shreds. The performance was repeated during subsequent runs.

Our next operation found us flooded by top officers and civilians from the Admiralty. Our antiaircraft gunnery was a primary reason ...”

The only time that DoY and Washington exercised AA fire together was:

From: 1200 April 6, 1942 to 1200 April 7, 1948.
(a) Moored in Scapa Flow.

(b) HMS Renown and USS WASP stood out. Commander-in-Chief, Home
Fleet, made official call on Comtaskfor 39. At 1113 underway in
company with DUKE OF YORK and six destroyers for gunnery practice.
OTC Vice-Admiral in DUKE OF YORK,. Steamed at various courses and
speeds in Flow operating area.

From: 1200 April 7, 1942 to 1200 April 8, 1942.

(a) Fired 80 rounds of 5"/38 anti-aircraft ammunition, AATP-S,
port and starboard batteries, at sleeve towed by British plane.
fired 1"1, 20mm, and .50 cal. machine gun batteries at sleeve.

DUKE OF YORK fired secondary battery at same sleeve. Total
ammunition fired: 806 rounds .50 cal., 514 rounds 20mm, 185
rounds 1"1. Starboard paravane line carried away. Recovered
paravane. Fired 48 rounds 5"/38 cal. at surface target, Day
Spotting Practice, following DUKE OF YORK on each run. Held
main battery tracking exercise on KENT. RAF Spitfires made
simulated attack to train lookouts, target designators, and
secondary battery. Held instruction of officers and mount cap-
tains of anti-aircraft battery in plane identification, using
British films of British and German planes. Moored to Buoy "E",
Scapa Flow, at 2114. Morning of 8th HMS VICTORIOUS stood in and
anchored. WICHITA and TUSCALOOSA stood out for gunnery practices.

(BB56 War diary)

So Hooper's memory was faulty as per the dates and the presence of WICHITA and TUSCALOOSA. No mention of the sleeve being shot down.

- - -

dunmunro,
You are far too conveniently selective, evasive and disingenuous in your responses; they constitute very unfortunate obstructions to any sort of honest and rational discussion.

Nothing you excerpted from the BB56 war diary whatsoever disputes Hooper's account in any way whatsoever. Read Musicant's operational history of USS Washington (which draws upon official USN operational and historical archives as well as numerous personal accounts of serving officers and crew. USS Washington arrived at Scapa Flow in the first week of April 42, but remained in the Scapa/Hvalfjord/Arctic Ocean are of operations through the PQ17 Murmansk run. Washington did not depart until mid-July 1942. Hooper was aboard her for the entire period - Apr-Jul 42. I'm guessing that you yourself have never seen, let alone read, Hooper's documents and reminiscences which officially reside in USN archives.

2)Why do you continue to wave Lundstrom around when you have the original USN AA analyses available? Have you bothered to distinguish between RN AA kills achieved by LAA and MAA (neither of which had anything to do with HACS or FKC) versus those actually effected by HACS/FKC controlled heavy AA? Have you bothered to read the HACS analyses by Pugh, Peat, Porteous or Marland? Have you bothered to compare the RPB figures for HACS/FKC versus contemporary Mk37 figures?

3)Are you aware that the US refused to release any of their VT fuze production for British HACS/FKC-equipped ships because evaluations had indicated that the effectively unstabilized HACS directors then in service were unable to reliably deliver fire within VT fuzing radius.

4)GRUDOU was a sufficient stop-gap solution, but was only put to paper at the end of 1942, prototype-tested in early 1943, and not fully fitted in the fleet until the end of 1944. VT ammunition was provided only to those ships with HACS directors fitted with GRUDOU stabilization. You could read about this in more detail than I am presenting if you had a copy of "From Fellside to Flyplane", but the self-publishing author sadly passed away in June of this year and the book is no longer available.


Byron

?????

You provided the information that stated "...the summer of 1942..." so if you have access to Hooper stating otherwise, please supply it. Hooper states: "...USS Tuscaloosa’s fire was close, Wichita’s highly accurate, ours tore the sleeve immediately to shreds..." But the only time that BB56 and DoY exercised AA together, those two cruisers were not present. Hooper's memory was faulty; this is a fact as I have conclusively proven.


2) The USN did not conduct an accurate assessment of own 5in AA efficacy during WW2. The only way to do this is to look at Lundstrom, and then tally his assessed AA kills versus the probable cause for each kill. When I did this for the 5 most modern MK37 equipped ships at Santa Cruz the numbers were pretty dismal... I readily admit that in both the RN and USN that the close range (CIWS) armament was by far the primary killer of aircraft. However, the number of USN 5in AA kills during 1942 is so low that HACS/FKC couldn't have been worse and whatever difference might have existed is more than offset by the lighter weight and lower topweight required for HACS/FKC which allowed for a much heavier CIWS.

3) Sources for that statement? The delays in designing a VT fuze for RN/UK guns had to do with the smaller diameter MT fuze that UK AA shells (UK 1.5in versus 2in for USN) were designed around and the different acceleration characteristics of UK/RN fixed case projectiles. Fuze production priority was: USN, RN, US Army, UK Army, according the The Deadly Fuze. From The Deadly Fuze: "...The British Navy received its first VT Mk33 fuzes in the summer of 1943. This was only half a year after the USN had begun using the Mk 32..." By Aug 15 1945 the RN had received ~840,000 operational VT fuzes and an additional ~50,000 for testing purposes.

Most HACS HADTs were stabilized in 1939 and by 1943 they all seem to have been.

4) GRUDOU was a late war development designed to give highly accurate short range FC to RN DP guns. It had nothing to do with the provision of VT ammo, which was issued to all ships, that had the requisite guns, by 1945. KGV's (and Argonaut's) RoP for Feb 1945 states the use of 5.25in VT ammo against a low flying attackers, but VT was ineffective in that case because the early VT fuze types were prone to prematures when fired at low angles over water. KGV did claim an HACS controlled 5.25in MT kill at ~10K yds against a low flying TE bomber, noting that Type 285P radar and her HADT observed the kill. Here HACT was operating in a special low angle target mode developed for HACS IV (possibly used in HACS III as well). KGV was sent east prior to the GRUDOU being fitted to HACS.

[wmh829386]

The difference between convoy battle and early pacific CV battles cannot be understated.
Firstly, PQ18 certainly has the advantage of only being attacked by Torpedo bombing and Glide Bombing. Dive bombing in the CV battle is much harder to target as you have noted. Secondly, the merchantman carries extra shortrange AA weapons. Considering the lack of light and medium AA of USN ships in 1942, PQ18's fire power shouldn't be underestimated. Thirdly, the short attack time in the CV battle is certainly a factor in the low number of AA kills! Being in a relentless wave of strikes also means there are more chances to shoot some enemy down. The fact that the strikes focus on a single target just put more pressure on the FC channels that can be saturated easily. Fourthly, having fighter cover reduces the number of bombers reaching the target.

If you look at it, the number of torpedo bombers getting through to the TF in Coral Sea and Midway isn't that big compare to the multiple sorties faced by PQ18. There's simply far more total number of targets available for PQ18 with the added benefit of have them arrive at a much longer time interval.

The problem of the HACT is not the accuracy of the projection screen, but that it does not update the target tracks correctly when a) it doesn't handle the change in height b) fictitious values is used to deal with spotting variables such as wind. If the system is totally reliant on GRU and radar to provide real-time information, it is, essentially, reduced to a Mk IV Pom-pom director with range plot and fuse clock. A long-range AA system relies on feed-back to show the operator whether his set-up is correct, but HACT was shown to be not suitable for that.

[Steve Crandell]

DoY didn't have to be present when the cruisers conducted the AA exercises. The practices could have taken place at different times, and Hooper's statement could still have been correct.

[dunmunro]

The difference between convoy battle and early pacific CV battles cannot be understated.
Firstly, PQ18 certainly has the advantage of only being attacked by Torpedo bombing and Glide Bombing. Dive bombing in the CV battle is much harder to target as you have noted. Secondly, the merchantman carries extra shortrange AA weapons. Considering the lack of light and medium AA of USN ships in 1942, PQ18's fire power shouldn't be underestimated. Thirdly, the short attack time in the CV battle is certainly a factor in the low number of AA kills! Being in a relentless wave of strikes also means there are more chances to shoot some enemy down. The fact that the strikes focus on a single target just put more pressure on the FC channels that can be saturated easily. Fourthly, having fighter cover reduces the number of bombers reaching the target.

If you look at it, the number of torpedo bombers getting through to the TF in Coral Sea and Midway isn't that big compare to the multiple sorties faced by PQ18. There's simply far more total number of targets available for PQ18 with the added benefit of have them arrive at a much longer time interval.

2)The problem of the HACT is not the accuracy of the projection screen, but that it does not update the target tracks correctly when a) it doesn't handle the change in height b) fictitious values is used to deal with spotting variables such as wind. If the system is totally reliant on GRU and radar to provide real-time information, it is, essentially, reduced to a Mk IV Pom-pom director with range plot and fuse clock. A long-range AA system relies on feed-back to show the operator whether his set-up is correct, but HACT was shown to be not suitable for that.

Longer drop range for Luftwaffe aircraft equals less effectiveness of naval CIWS and more reliance on HACS/FKC and it follows from that that a higher proportion of RN AA kills would come from HACS/FKC.

CIWS at Santa Cruz and BuOrd awarded kills:

USS South Dakota 16 x 40mm; 4000 rnds fired, 20 x 1.1in; 3000 rnds fired and ~58 x 20mm ( from her Action Report: 52000 20mm rounds fired at 900rpg ) (26 awarded kills)

USS Hornet - 20 x 1.1mm ~5050 rnds fired and 32 x 20mm; ~18600 rnds fired. (Friedman US Aircraft Carriers and Hornet AR) (25 awarded kills)

USS Enterprise 16x 40mm; 3200 rnds fired, 4 x 1.1in; 500 rnds fired, and 44 x 20mm; 46000 rnds fired (CV6 website) (30 awarded kills)

The increase in USN CIWS at Santa Cruz was considerable and these 3 ships fired over 116000 rnds of 20mm and ~16000 rnds of 40mm and 1.1in. The 3 ships were awarded 81 (64%) of the 127 awarded AA kills. Divide the BuOrd numbers by 5 to get an approximation of actual kills per ship. Despite the increase in Mk37 equipped ships 5in AA was a non-factor at Santa Cruz.

2) You continue to ignore operational effectiveness and prefer to focus on something that was a non-issue. Both Mk33/37 and HACS/FKC had similar issues when they had to rely on optical ranging. You ignore the ability of the HADT and HACT's crews to operate their equipment in combat and produce effective fire on real targets and that is the crux of the issue. In 1942 Mk33 and Mk37 performed very poorly and the available evidence is that HACS/FKC out performed it. The greater use of radar with HACS/FKC was probably the main reason for this, but even when radar was added to Mk33/37 there was no increase in operational effectiveness in 1942.

[dunmunro]

DoY didn't have to be present when the cruisers conducted the AA exercises. The practices could have taken place at different times, and Hooper's statement could still have been correct.

Hooper stated that that BB56, DoY and the two cruisers conducted AA exercise together, but they didn't. Hooper's memory was faulty.

If someone recounted their experiences at Denmark Straits, but claimed that ships were there they weren't, how much stock would you put in their recollections?

[dunmunro]

This data is drawn from THE APPLICATIONS OF RADAR AND OTHER ELECTRONIC SYSTEMS IN THE ROYAL NAVY IN
WORLD WAR 2. Monograph 2 Weapon Control in the Royal Navy,1935-45, by H. W. Pout(*)

Pout analysed HACS theoretical performance using (AFAICT) 4in ammo. He started his analysis by looking at RN AA performance in Norway and increased system aiming errors for various parameters to match the observed results. His analysis assumes a single 180 knot target at a present range of 7.6, 5.2, and 4.0 thousands of yards and a predicted range of 6, 4, and 3 thousand yards, with a 6 sec dead time:

Case 1: kill probability (no radar assistance HACS 1)

Rf(kyds)/Rp(kyds) Tp(ToF + 6 sec DT in secs) shell velocity at target (yds/sec) Pk (Rounds Per Kill )
6 / 7.6 / 16 / 440 1 in 10000 shots
4 / 5.2 / 12 / 500 1 in 3200 shots
3 / 4 / 10 / 600 1 in 2000 shots

He then looks at probable performance with these advances in FC:

Case 2: kill probability (Type 285P radar HACS 3).

6 / 7.6 / 16 / 440 1 in 2800 shots
4 / 5.2 / 12 / 500 1 in 1800 shots
3 / 4.0 / 10 / 600 1 in 1500 shots

Case 3: kill probability (GRU and Type 285P radar HACS 4).

6 / 7.6 / 16 / 440 1 in 2100 shots
4 / 5.2 / 12 / 500 1 in 1400 shots
3 / 4.0 / 10 / 600 1 in 1100 shots

( Case 4: VT ammo kill probability / Case 2 FC / Case 3 FC. (this VT data included for reference)

6 / 7.6 / 10 / 440 / 1 in 250 shots / 1 in 185 shots
4 / 5.2 / 6 / 500 / 1 in 70 shots / 1 in 50 shots
3 / 4.0 / 4 / 600 / 1 in 40 shots / 1 in 30 shots )


When I look at actual Mk33/37 performance in the Pacific in 1942. I find that the rounds per kill is a good match to Pout's numbers for HACS without radar. This is not surprising as HACS and Mk33/37 computer prediction assumes straight line flight, at a constant speed, and this is seldom the case for actual aircraft. Pout's number are unduly pessimistic for gunnery practise with target drones, drogues and against aircraft that actually fly a straight line course, especially if radar ranging is used.


(*)" H.W. Pout, CB, aBE, BSc (Eng), FCGI, flEE, FBIM, graduated from
Imperial College, London, in 1940 and immediately joined HM Signal
School, working initially on direction-finding. Subsequently he joined the
Gunnery Radar Group (under J. F. Coales), then in the early stages of
expansion. From then until 1954 he specialised in gun and then guided weapon
radar-control systems. This was followed by four years in Naval
operational research, one year at the Imperial Defence College and five
years as Head of Guided Weapons Projects, Admiralty. In 1965 he
became Assistant Chief Scientific Adviser (Projects) in the Ministry of
Defence in 1969; Director of the Admiralty Surface Weapons Establishment
(descended from HM Signal School); from 1973 he filled a number
of Deputy Controllership appointments in the Ministry of Defence, the
Army Department and the Air Force Department. Following retirement
from the Civil Service he was engaged in private consultancy work for a
period, before undertaking a final appointment with GEC. He was
awarded a CB and an OBE for his services."

[Steve Crandell]

DoY didn't have to be present when the cruisers conducted the AA exercises. The practices could have taken place at different times, and Hooper's statement could still have been correct.

Hooper stated that that BB56, DoY and the two cruisers conducted AA exercise together, but they didn't. Hooper's memory was faulty.

If someone recounted their experiences at Denmark Straits, but claimed that ships were there they weren't, how much stock would you put in their recollections?

So you think this mistake means what? That DoY shot better than Washington?

[dunmunro]

DoY didn't have to be present when the cruisers conducted the AA exercises. The practices could have taken place at different times, and Hooper's statement could still have been correct.

Hooper stated that that BB56, DoY and the two cruisers conducted AA exercise together, but they didn't. Hooper's memory was faulty.

If someone recounted their experiences at Denmark Straits, but claimed that ships were there that weren't, how much stock would you put in their recollections?

So you think this mistake means what? That DoY shot better than Washington?

It means that Hooper's memory (as we know via the BB56 war diary) was faulty and that 22 years after the fact he got it wrong. I don't know what he saw, only that his account doesn't match the war diary, which was recorded right at the time the events were happening. BTW, I read through every BB56 WD entry from April to July 1942, and there was only one occasion when BB56 and DoY had joint AA practise.

DoY had essentially the same FC as Scylla. We have one of Scylla's GO's stating that they were able to shoot down drogues and that he personally shot one down on his first trial:

https://www.world-war.co.uk/scylla_story.php

So what are we to make of all this? Is Hooper's recollection really significant?

[wmh829386]

The difference between convoy battle and early pacific CV battles cannot be understated.
Firstly, PQ18 certainly has the advantage of only being attacked by Torpedo bombing and Glide Bombing. Dive bombing in the CV battle is much harder to target as you have noted. Secondly, the merchantman carries extra shortrange AA weapons. Considering the lack of light and medium AA of USN ships in 1942, PQ18's fire power shouldn't be underestimated. Thirdly, the short attack time in the CV battle is certainly a factor in the low number of AA kills! Being in a relentless wave of strikes also means there are more chances to shoot some enemy down. The fact that the strikes focus on a single target just put more pressure on the FC channels that can be saturated easily. Fourthly, having fighter cover reduces the number of bombers reaching the target.

If you look at it, the number of torpedo bombers getting through to the TF in Coral Sea and Midway isn't that big compare to the multiple sorties faced by PQ18. There's simply far more total number of targets available for PQ18 with the added benefit of have them arrive at a much longer time interval.

2)The problem of the HACT is not the accuracy of the projection screen, but that it does not update the target tracks correctly when a) it doesn't handle the change in height b) fictitious values is used to deal with spotting variables such as wind. If the system is totally reliant on GRU and radar to provide real-time information, it is, essentially, reduced to a Mk IV Pom-pom director with range plot and fuse clock. A long-range AA system relies on feed-back to show the operator whether his set-up is correct, but HACT was shown to be not suitable for that.

Longer drop range for Luftwaffe aircraft equals less effectiveness of naval CIWS and more reliance on HACS/FKC and it follows from that that a higher proportion of RN AA kills would come from HACS/FKC.

CIWS at Santa Cruz and BuOrd awarded kills:

USS South Dakota 16 x 40mm; 4000 rnds fired, 20 x 1.1in; 3000 rnds fired and ~58 x 20mm ( from her Action Report: 52000 20mm rounds fired at 900rpg ) (26 awarded kills)

USS Hornet - 20 x 1.1mm ~5050 rnds fired and 32 x 20mm; ~18600 rnds fired. (Friedman US Aircraft Carriers and Hornet AR) (25 awarded kills)

USS Enterprise 16x 40mm; 3200 rnds fired, 4 x 1.1in; 500 rnds fired, and 44 x 20mm; 46000 rnds fired (CV6 website) (30 awarded kills)

The increase in USN CIWS at Santa Cruz was considerable and these 3 ships fired over 116000 rnds of 20mm and ~16000 rnds of 40mm and 1.1in. The 3 ships were awarded 81 (64%) of the 127 awarded AA kills. Divide the BuOrd numbers by 5 to get an approximation of actual kills per ship. Despite the increase in Mk37 equipped ships 5in AA was a non-factor at Santa Cruz.

2) You continue to ignore operational effectiveness and prefer to focus on something that was a non-issue. Both Mk33/37 and HACS/FKC had similar issues when they had to rely on optical ranging. You ignore the ability of the HADT and HACT's crews to operate their equipment in combat and produce effective fire on real targets and that is the crux of the issue. In 1942 Mk33 and Mk37 performed very poorly and the available evidence is that HACS/FKC out performed it. The greater use of radar with HACS/FKC was probably the main reason for this, but even when radar was added to Mk33/37 there was no increase in operational effectiveness in 1942.

You have admitted that the attack profile of during PQ 18 is biased towards heavy AA while at the same time dismissing the possiblity that such difference plays a big role of how Mk37 performed poorly.
It is probably a good time to bring up the POW, the attack it faced resemble much more closely to what the US CV experienced, but no torpedo bombers are shot down by the HACS. if we look at the record of the PQ 18 naively, it should have scored kills given how fragile IJN planes are and that the engagement starts before any torpedo hit the water. Another example is Operation Pedestal where HACS did very little, Or the time when in Mediterranean when HMS Formidable was bombed. I am not ignoring operation effectiveness, it is just that it doesn't show that HACS as being more effective than MK37.
Let me put it bluntly, nobody could find out what actually happened in the director towers during the early CV battle, was radar range used? Was it in rate control or automatic? Did the directors received target information in time? What we could do is look at the technical aspect of the system and see that it performs well with the arrival of Radar and VT fuse, more so than the HACS after 1942 and that mechanically the Mk37 changed less compared to the HACS 3 to HACS 6 in the same period. This suggested that the poor performance in 1942 is less about the core mechanism of the Mk37/Mk1 but the circumstances that surrounded it.

[dunmunro]

The difference between convoy battle and early pacific CV battles cannot be understated.
Firstly, PQ18 certainly has the advantage of only being attacked by Torpedo bombing and Glide Bombing. Dive bombing in the CV battle is much harder to target as you have noted. Secondly, the merchantman carries extra shortrange AA weapons. Considering the lack of light and medium AA of USN ships in 1942, PQ18's fire power shouldn't be underestimated. Thirdly, the short attack time in the CV battle is certainly a factor in the low number of AA kills! Being in a relentless wave of strikes also means there are more chances to shoot some enemy down. The fact that the strikes focus on a single target just put more pressure on the FC channels that can be saturated easily. Fourthly, having fighter cover reduces the number of bombers reaching the target.

If you look at it, the number of torpedo bombers getting through to the TF in Coral Sea and Midway isn't that big compare to the multiple sorties faced by PQ18. There's simply far more total number of targets available for PQ18 with the added benefit of have them arrive at a much longer time interval.

2)The problem of the HACT is not the accuracy of the projection screen, but that it does not update the target tracks correctly when a) it doesn't handle the change in height b) fictitious values is used to deal with spotting variables such as wind. If the system is totally reliant on GRU and radar to provide real-time information, it is, essentially, reduced to a Mk IV Pom-pom director with range plot and fuse clock. A long-range AA system relies on feed-back to show the operator whether his set-up is correct, but HACT was shown to be not suitable for that.

Longer drop range for Luftwaffe aircraft equals less effectiveness of naval CIWS and more reliance on HACS/FKC and it follows from that that a higher proportion of RN AA kills would come from HACS/FKC.

CIWS at Santa Cruz and BuOrd awarded kills:

USS South Dakota 16 x 40mm; 4000 rnds fired, 20 x 1.1in; 3000 rnds fired and ~58 x 20mm ( from her Action Report: 52000 20mm rounds fired at 900rpg ) (26 awarded kills)

USS Hornet - 20 x 1.1mm ~5050 rnds fired and 32 x 20mm; ~18600 rnds fired. (Friedman US Aircraft Carriers and Hornet AR) (25 awarded kills)

USS Enterprise 16x 40mm; 3200 rnds fired, 4 x 1.1in; 500 rnds fired, and 44 x 20mm; 46000 rnds fired (CV6 website) (30 awarded kills)

The increase in USN CIWS at Santa Cruz was considerable and these 3 ships fired over 116000 rnds of 20mm and ~16000 rnds of 40mm and 1.1in. The 3 ships were awarded 81 (64%) of the 127 awarded AA kills. Divide the BuOrd numbers by 5 to get an approximation of actual kills per ship. Despite the increase in Mk37 equipped ships 5in AA was a non-factor at Santa Cruz.

2) You continue to ignore operational effectiveness and prefer to focus on something that was a non-issue. Both Mk33/37 and HACS/FKC had similar issues when they had to rely on optical ranging. You ignore the ability of the HADT and HACT's crews to operate their equipment in combat and produce effective fire on real targets and that is the crux of the issue. In 1942 Mk33 and Mk37 performed very poorly and the available evidence is that HACS/FKC out performed it. The greater use of radar with HACS/FKC was probably the main reason for this, but even when radar was added to Mk33/37 there was no increase in operational effectiveness in 1942.

1)You have admitted that the attack profile of during PQ 18 is biased towards heavy AA while at the same time dismissing the possiblity that such difference plays a big role of how Mk37 performed poorly.

2)It is probably a good time to bring up the POW, the attack it faced resemble much more closely to what the US CV experienced, but no torpedo bombers are shot down by the HACS. if we look at the record of the PQ 18 naively, it should have scored kills given how fragile IJN planes are and that the engagement starts before any torpedo hit the water.
2A)Another example is Operation Pedestal where HACS did very little, Or the time when in Mediterranean when HMS Formidable was bombed. I am not ignoring operation effectiveness, it is just that it doesn't show that HACS as being more effective than MK37.

3) Let me put it bluntly, nobody could find out what actually happened in the director towers during the early CV battle, was radar range used? Was it in rate control or automatic? Did the directors received target information in time?
3A)What we could do is look at the technical aspect of the system and see that it performs well with the arrival of Radar and VT fuse, more so than the HACS after 1942 and that mechanically the Mk37 changed less compared to the HACS 3 to HACS 6 in the same period. This suggested that the poor performance in 1942 is less about the core mechanism of the Mk37/Mk1 but the circumstances that surrounded it.

1) At Santa Cruz Mk37 was present in the USN's most modern ships and they all had Mk4 FD radar, which theoretically should have allowed for long range tracking and blind fire yet Mk37 and FD radar failed almost completely. At Santa Cruz the IJNAF sent a formation of level bombers (Kates equipped with 800kg bombs) to attack Hornet yet even radar equipped Mk37 guns were unable to engage the formation effectively. We have discussed how a large formation of USN ships, all but one of which had a HA FC system, failed to place accurate fire on the IJN bomber formations at Bougainville.

2) Force Z consisted or PoW with HACS IV GB, but with only partially functioning FC radars. Repulse had HACS 1 or 2 and a rather elderly fit of 6 x 4in AA guns, whilst none of the 4 destroyers had any HA FC system. Here's the results of HACS engaging the first 8 level bomber attack sorties:

When they released their bombs, the Japanese planes were seen to surge upwards like a flock of birds, and then to fly steadily away to the north. The high-angle guns of both ships and of the destroyers continued to fire for a few moments, but then stopped to conserve ammunition. Prince of Wales’s single Bofors guns, mounted on the quarterdeck and manned by Royal Marines, had opened fire and even her pom-poms had let off a few defiant rounds when the Japanese had been directly overhead though still out of the pom-poms’ range. The 5.25-in. guns of Prince of Wales had fired 108 rounds and the 4-in. guns of Repulse thirty-six rounds. The British gunners were probably disappointed at failing to shoot down any of the Japanese, but they had actually done quite well. No less than five of Lieutenant Shirai’s eight aircraft had been hit by the fire, two so seriously that they left the scene of action and flew straight back to their airfield. (Middlebrook and Mahoney, Battleship; their data on IJNAF aircraft damage was drawn from IJ official sources)

One of the IJNAF aircraft that was forced to abort crash landed and was destroyed, and was therefore an AA kill. It was most probably hit by PoW's 5.25in guns. In the initial attacks PoW's HACS was hampered by the fact that the ships were often maneuvering under full helm, which was a similar complaint raised by the Mk37 crews at Santa Cruz. Against the torpedo bombers PoW's HACS did poorly, but this is not surprising given the short time of the engagement and the relatively small number of 5.25in rounds fired (12 salvos with predicted fire and more in barrage fire for maybe a 150-200 rounds fired). Additionally, the IJNAF aircraft flew a curved course down to release altitude. This is what Yorktown reported when trying to engage TBs at Midway:

At 1359 Radar reported enemy planes bearing 250° true. When this group was about 17 miles away they were attacked by our fighters. Several were shot down and as the dog fight approached, it could be seen that the attack group was broken up. However, one at a time, seven planes were seen to break away and approach the ship, altitude about 12,000 feet, slant range about 8,000 to 10,000 yards. The forward director took control of the starboard 5" battery and opened fire on these planes. This fire was ineffective since the planes circled or approached their diving points by a curved path.
http://www.ibiblio.org/hyperwar/USN/shi ... idway.html

But of course Yorktown was screened by 4 cruisers and 7 destroyers during the TB attack, all but one of which has AA FC systems and all the destroyers save Balch had Mk 37. Rather tragically, both PoW and Repulse had severe problems with their octuple pom-poms due to apparently defective ammunition, which caused multiple gun jams on both ships. But the only way that the TB attack could have been countered by AA would have been via the addition of a large screen of modern cruisers and destroyers.

2A) HACS/FKC did what it was designed to do at Pedestal and it did score some kills. Almost all the merchant ships losses occurred after the main body of the RN ships turned back, (dictated by the geography of the area) leaving a much reduced surface ship force to escort the merchant ships into Malta. In May 1941 there were very few AA FC radars installed in the fleet, whereas by mid 1942, they were almost universal, even on destroyers. However, as we've discussed, Mk33/37 were very heavy and used up a lot of the available topweight, therefore, they would have to perform better than HACS/FKC to justify their operational costs, and in 1942, Mk33/37 didn't perform better.

3) Bluntly put, I have read the action reports of all the USN ships present during the USN's 1942 carrier antiaircraft engagements. The universal complaint was that director tracking was near useless, FD radar was near useless, and there were several recommendations by Yorktown and Hornet to remove the entire 5in battery from the carriers along with it's ineffective MK33/37 FC systems. This is from Enterprise's AR at Santa Cruz:

DEFENSE BY ANTI-AIRCRAFT BATTERIES
Again fire control radar did not pick up any target. At no time since its installation has it been useful. Previously submitted recommendations relative to its modification are again stressed. The precision requirements necessary to put this equipment on an aerial target apparently cannot be met in action.
Neither 5-inch director picked up targets, although the rangefinder in Sky Forward was able to do so.
Complete power failures occurred on Groups I and II 5-inch. Partial power failure occurred on Group III. There were frequent rammer failures and electrical misfires on all guns.
The apparently unwieldy director firing system, augmented by numerous casualties which greatly slow the rate of fire, has made the 5-inch battery the least useful of the AA for all except high altitude horizontal bombing attacks. In local control, difficulty is experienced in getting both trainer and pointer on the same target. A new type of fuze, which it is understood will soon be available, may greatly increase the effectiveness of the 5-inch against dive bombing and torpedo attacks. http://www.cv6.org/ship/logs/action1942 ... onclusions

Friedman has this to say about dual purpose guns:

In 1939 the standard antiaircraft guns of the destroyer force were the dual-purpose 5-in./38, the 1.1-inch machine cannon (mounted only in the 1,850-ton leaders" with their single-purpose 5-inch guns), and the .50-caliber water-cooled machine gun. In theory, the 5-inch gun could counter either horizontal or torpedo bombers; it could not fire nearly fast enough to present any threat to dive bombers, which, ironically, were probably the most lethal threat to fast, maneuverable craft such as destroyers. However, it could be argued that in practice the dive bombers would go for larger and more lucrative targets, and that the machine cannon effective against them had ranges far too short to allow screening destroyers to provide protection. Finally, the .50-caliber was considered effective against strafers trying to break up the antiaircraft barrage that the destroyer screen might try to erect around the battle fleet. In an important sense the choice not to arm U.S. fleet destroyers with the 1.1-inch gun was a choice for antidestroyer over antiaircraft firepower, a choice in favor of classical battle line concepts.
War experience soon showed the immense value of the heavy automatic cannon... (US Destroyers p203)

RN DP AA guns were no better at countering divebomber attacks, but at least the lightweight FKC allowed for the installation of an autocannon CIWS on RN destroyers. The ABU was designed to allow for a short range zero deadtime engagement of aircraft and it became available in late 1942.

3a) MK37 received dozens of mods between 1942 and 1945 including many for Mk1 computer was also extensively modified, especially it's rate control mechanisms. This was just one of the issues in the wartime Mk1 computer:

During problem solutions, a large, quick change in target angle may cause the rate-control mech-
anism to begin to compute an erroneous solution in which target angle is 180° from the correct
value, and target speed is negative. This is evidenced by a sudden decrease in target speed to some
fictitious value below 100 knots and then a cessation of rate corrections. This false solution can be
overcome by holding the target-speed switch at increase until target speed reaches its former value.
(Naval Ordnance and Gunnery 1944)

In 1947 all the mods were incorporated into the Mk1A computer along with a completely revamped rate control system.