Tribal class dd

[Steve Crandell]

[

Why again is the Mark 37 not capable of this? It never shot down any aircraft in comparable circumstances?

Oh, and how was the HACS at surface fire control?

I have no doubt that Mk 37 was capable of it, but the fact is that many people think that HACS wasn't. The only advantage that HACS would have over Mk 37 (assuming it had time to come to solution via automatic rate control) was that HACS had better control over dead time and thus more accurate fuze timing.

HACS/FKC was always paired with an AFCC or a FCB, although the HACS/FKC had a minimal ability to engage surface targets.

So it took two different directors to achieve what the Mark 37 did with one?

[alecsandros]

The USN introduced VT ammo in Jan 1943.

Attacking fleet carriers (with large numbers of embarked fighters and fighter capable SBDs) with small numbers of highly flammable, and comparatively slow IJN TE bombers was a losing proposition for the IJN. However, attacks by large numbers of Ju-88s combined with He-111 torpedo bombers was a much tougher proposition for the defence and the USN said so. The USN considered Luftwaffe aircraft superior to IJN aircraft ( see my post of Tue Oct 07, 2014 10:52 pm) - and they were;

There is little doubt that the German torpedo bombers were more resilient than the Japanese ones.

However, we should observe that the USN torpedo bombers were also stronger than the Japanese ones, but still suffered great casualty rates in all major carrier battles of 1942.

From USS Enterprise action report after Santa Cruz:

"The limitations in the use of torpedo planes, which have repeatedly been set forth in reports of previous actions, were again amply demonstrated. Although the attack of the enemy torpedo squadron (probably 18 planes) against the ENTERPRISE was executed with obvious skill and great determination, only about nine planes reached a proper release point, and no hits were made. The harassing effect on the Japanese pilots of the extremely heavy and accurate fire of the combined task force and the maneuvers of the ship in combing the wakes of the torpedoes launched were the prime factors in nullifying the attack. The results of the attacks of our own torpedo planes, while not nil, were disappointing. It has been proven time and again that the probability of success of a torpedo plane attack in good visibility against a formation properly defended by fighters and anti-aircraft fire is small and out of all proportion to the losses in planes and men. The conclusion is obvious - that in the present state of the art, torpedo plane operations should if practicable be limited to attacks delivered under conditions of low visibility or in mopping up operations after the defensive power of the enemy formation has been reduced. Thus limited, the torpedo plane is not as valuable, plane for plane, in day operations as is the dive bomber. Accordingly, it is recommended that for the present, the air groups of our large carriers include not more than twelve torpedo planes. Only when torpedo squadron personnel are fully trained and planes are equipped for all aspects of night operations will torpedo planes reach their full effectiveness. We should not abandon them for carrier use; after all, they were the decisive factor in the HORNET attack."

http://www.cv6.org/ship/logs/action19421026.htm#action

[alecsandros]

Duncan,

I read more about PQ-18.

My dear, those Hunt Class and M-class destroyers had over 12 AA guns each, including 6 heavy AA guns. The other destroyers had between 4 and 8 guns of 20mm and above.

That's some serious firepower.

Do you have an estimate of the total AA artillery mounted on board the British ships ?
My numbers are for Scylla , Alynbank and Ulster Queen - 24 x 4/4.5" guns, and about 28 x pom poms and 20mm mounts. CVE Avenger had about 20 x 20mm and pom poms.

[dunmunro]

[

Why again is the Mark 37 not capable of this? It never shot down any aircraft in comparable circumstances?

Oh, and how was the HACS at surface fire control?

I have no doubt that Mk 37 was capable of it, but the fact is that many people think that HACS wasn't. The only advantage that HACS would have over Mk 37 (assuming it had time to come to solution via automatic rate control) was that HACS had better control over dead time and thus more accurate fuze timing.

HACS/FKC was always paired with an AFCC or a FCB, although the HACS/FKC had a minimal ability to engage surface targets.

So it took two different directors to achieve what the Mark 37 did with one?

No, it took two different FC computers. Many (actually all) directors using HACS/FKC were dual purpose as they could feed LA info to the LA computer, although the same ship (Tribal class for example) might have a dedicated LA director with better LA FC gear where some ( Hunt class destroyer, for example) had a combined HA/LA DCT. However the combined weight of two RN directors (HADT and DCT) was still considerably less than the Mk 37 DCT.

[dunmunro]

Duncan,

I read more about PQ-18.

My dear, those Hunt Class and M-class destroyers had over 12 AA guns each, including 6 heavy AA guns. The other destroyers had between 4 and 8 guns of 20mm and above.

That's some serious firepower.

Do you have an estimate of the total AA artillery mounted on board the British ships ?
My numbers are for Scylla , Alynbank and Ulster Queen - 24 x 4/4.5" guns, and about 28 x pom poms and 20mm mounts. CVE Avenger had about 20 x 20mm and pom poms.

The Tribal class had similar AA firepower. I don't have an estimate for all ships, but you have to remember that the convoy screen was spread over many miles so that the total firepower could never be used to defend a single target.

Ulster Queen carried 6 x 4in (3 x twin mounts).

[alecsandros]

The Tribal class had similar AA firepower. I don't have an estimate for all ships, but you have to remember that the convoy screen was spread over many miles so that the total firepower could never be used to defend a single target.

Ulster Queen carried 6 x 4in (3 x twin mounts).

true,
from the dispositions it seems that about half of the escorts were concentrated immediately around the convoy (which occupied a box of 3 x 5 km)

[dunmunro]

It's interesting how you convert the integral hoist/fuse setter into a disadvantage because the USN doesn't have to wait for a "load lamp".

Every advantage of the Mark 37 system you try to turn into a disadvantage. Too bad Vanguard was hobbled with that horrible kluge.

Here's the deadtime calculation done by the Mk 1 computer:

http://www.hnsa.org/doc/computermk1/pg288.htm

It's pretty obvious that loading variations between gun crews will increase pattern size. By the time Vanguard appeared, VT ammo was the norm and deadtime no longer mattered so much, although without a metadyne fuze setter manual and the manual for the RN modded Mk1 computer, there's no way to know if the RN modded the Mk1 to include a load lamp.

Some info on Mk 37 deadtime:

This exciting episode was our introduction to the battlefield performance of America's latest miracle weapon, the VT (variable time) fuse, also (and more meaningfully) called the "influence" or "proximity" fuse. For larger caliber antiaircraft guns like the 5-inch/38, which seeks to destroy a plane with shrapnel by exploding a shell near the target, the VT fuse eliminated what was by far the greatest difficulty—getting the shell to explode at just the right time— neither too soon before reaching the target, nor too late after passing it. Ordinary fuses were preset at the gun and then loaded into the gun by human hands. The biggest, strongest man was always chosen to lift the 54-pound shell and place it on the loading tray of the gun. I have seen an officer with a stopwatch seeking to establish the exact time interval between setting the fuse and loading the shell. Each loader took a different time and, indeed, could not be expected to be consistent each time. Where timing was everything, room for error was monumental.
From Dam neck to Okinawa
http://www.ibiblio.org/hyperwar/USN/rep ... index.html

The inability to control deadtime is a glaring fault of the Mk 37 system.

[Byron Angel]

Re the HACS versus Mk37 issue, readers with an interest to get an objective assessment are recommended to read the Admiralty wartime PiNGs, Friedman's recent book on AA, DK Brown's "Nelson to Vanguard" and Edgar March's "British Destroyers".

B

[Steve Crandell]

Maybe you folks can help me understand how HACS worked.

As I understand it, one would try to determine a spot in space where the target was going to be at a certain point in time. The fuse setters were set to that range. Then the guns were all loaded. Then the fire contol person waited until the target was at a point where it would arrive at the point in space at the same time as the shells (assuming no course changes in the interim), and all the guns were fired. Then a now future location was computed and the process was completed. Obviously firing would not be continuous and would be rather slow and methodical. Is that pretty much how it worked?

My question is, without a tachymetric system, how did one compute where the target was going to be at that hypothetical future time?

With the Mark 37 system, it attempted to continuously compute where the target was going to be and all the guns were loaded and fired as fast as possible. It was extremely wasteful due to dead time and other factors, but the volume of fire was so great that every so often an aircraft would arrive somewhere at the same time as a shell.

If I am correct, the US system was very inefficient but would be likely to shoot down more aircraft simply due the the large number of rounds being thrown out there. The British system would use much less ammo but would also shoot down fewer aircraft. It might look more efficient in terms of how many rounds it took to down an aircraft, though. The Mark 37 was capable of doing the same thing, but the USN chose not to and preferred the much higher rate of fire. I think that was partly because a perfect solution would never work if the target jinked, where if you just throw a lot of ammunition into the target's vicinity the laws of probability are going to help you.

[dunmunro]

The only way to do an objective assessment of RN AA is to do a comparative analysis of it in comparison to other WW2 naval AA systems. This was not possible during WW2 and even for many years after, because the basic data of how well the USN systems performed was completely distorted. Friedman gives us hints that using pre-war drone testing, that the two were more alike than not. What he doesn't do is look at similar AA actions, and then study how well one system performed versus another.

Again, the RN complaining about their AA capability is not a proper analysis, since they had no objective basis to decide on whether what they had was better or worse than what others had.

One thing that we can do from the perspective of 70 years on, is to look at some basic parameters of HACS and FKC:

1) could HACS/FKC produce accurate outputs from accurate inputs? IE, was it capable of producing bursts close to an aircraft with MT ammo when given accurate input parameters for target range, altitude, speed and direction?

2) Was HACS/FKC capable of generating accurate target parameter inputs? Are there examples of this in drone firings and in combat? What factors hindered good input data?

3) how quickly could HACS/FKC produce a FC solution and was this a factor in it's selection over tachymetric systems? What other factors existed that led to HACS/FKC being selected?

4) How did HACS/FKC compare in terms of weight, volume, cost and complexity with other naval AA systems and what comparative advantages/disadvantages flowed from this?

4) what were HACS/FKC's known limitations and what, if any measures were developed to overcome these in combat?

5) Did differences of opinion exist within the RN AA establishment over the theoretical and operational requirements for effective AA gunnery? What were those different opinions and what was the basis for these differences?

I've touched on several factors which can be used to develop a proper comparative analysis. It can be done but usually isn't.

[Byron Angel]

Another option is to consult contemporary archival documents (PiNGs for example), writings of those who were professionally involved with such matters (DK Brown for example), studies of academics with the necessary scientific credentials (N Friedman, D Mindell) and proper historians granted access to relevant official archives (such as E J March).

Strictly my opinion, of course.

B

[dunmunro]

Maybe you folks can help me understand how HACS worked.

As I understand it, one would try to determine a spot in space where the target was going to be at a certain point in time. The fuse setters were set to that range. Then the guns were all loaded. Then the fire contol person waited until the target was at a point where it would arrive at the point in space at the same time as the shells (assuming no course changes in the interim), and all the guns were fired. Then a now future location was computed and the process was completed. Obviously firing would not be continuous and would be rather slow and methodical. Is that pretty much how it worked?

My question is, without a tachymetric system, how did one compute where the target was going to be at that hypothetical future time?

With the Mark 37 system, it attempted to continuously compute where the target was going to be and all the guns were loaded and fired as fast as possible. It was extremely wasteful due to dead time and other factors, but the volume of fire was so great that every so often an aircraft would arrive somewhere at the same time as a shell.

If I am correct, the US system was very inefficient but would be likely to shoot down more aircraft simply due the the large number of rounds being thrown out there. The British system would use much less ammo but would also shoot down fewer aircraft. It might look more efficient in terms of how many rounds it took to down an aircraft, though. The Mark 37 was capable of doing the same thing, but the USN chose not to and preferred the much higher rate of fire. I think that was partly because a perfect solution would never work if the target jinked, where if you just throw a lot of ammunition into the target's vicinity the laws of probability are going to help you.

Mk 37: the DCT team input range, bearing, altitude and estimates of target speed and rate of altitude change to the Mk 1 computer. The DCT team then held their sights on the target and pressed a key which caused the computer to generate an estimate of target motion, and fed this info back to the DCT. if the DCT team had to override the computer's solution it caused an error signal, which forced the computer to generate new estimates of target motion until, eventually, the computer's estimate matched the target's actual motion. The GCO would then open fire. Unfortunately, if a match between the computer's estimate and actual target motion failed to occur, for example, because the target wasn't flying a straight line course then Mk 37 wouldn't open fire.

HACS: The DCT team input range, bearing, altitude, GCO measured target direction and GCO estimates of target speed to the HACS Table. The table would then produce an estimate of the where the target would be based upon the geometry of the inputs, and the GCO would then open fire. The Table would also pass the generated range rate to the rangefinder, so that the RF operator could make adjustments if the two didn't match. The GCO then issued spot corrections based upon AA bursts and observed target motion. The GCO would feed the the Table with false info if the target wasn't flying a straight line course at a steady altitude, and this info was chosen so that the Table would hopefully produce an accurate output and keep the bursts on the target.

This is a very quick and dirty summation, but the essence of it is, that it was HACS/FKC which tried to generate the maximum volume of fire, ASAP, while MK 37 was theoretically more methodical.

more later.

[dunmunro]

Of course, the tendency for Mk 37 not to open fire meant that USN ammo expenditure tended to be quite low, especially on destroyers. In time, USN GCOs began to modify Mk 37 doctrine and they would open fire based upon their initial, partially guessed, inputs (just as per HACS/FKC) while still trying to use the Mk1 computer to generate a more accurate solution, but most pilots knew that flying straight and level while under fire was highly unhealthy so accurate computer solutions were not that common.

The RN stressed the importance of opening fire quickly, with a very high volume of fire, hence the very high rates of ammo expenditure in the RN. The high rates of ammo expenditure in the RN, along with relatively small numbers of AA claims seemed to compare very unfavourably with the USN, where a smaller volume of fire seemed to be producing much better results.

We know from Friedman's RN Cruisers, that the RN purposely turned down tachymetric AA FC in favour of a geometric (goniometric) system precisely because they knew that tachymetric systems would be not be able to produce a solution against a manoeuvring target.

HACS used a dual system to produce the firing solution. Inputs of target speed, direction, altitude and range were used to create a two dimensional display on the HACS deflection screen. The intersection of deflection and elevation cursors with current target position (based upon the DCT inputs) was used to predict the future position of the aircraft. This process computed via graphical display, rather than by purely mechanical computation, and consequently produced a very rapid solution. Fuze timing was determined via aligning a cursor with a paper plot (this was done differently in FKC) with the slope of the plot changing with the range rate. The plot was able to display inputs from the optical RF range rate, radar range rate and a generated (smoothed) rate created by averaging all range, altitude, and target bearing inputs and the HACP team would decide which rate was most accurate and use that (typically radar if available), to determine ToF to the target, which along with deadtime produced the time setting output to the MT fuze setters. A clockwork mechanism would light a predict lamp and then a load lamp to tell the fuze setter and loader when to do their respective jobs, finally a fire lamp would light to tell the GCO when to fire, but I believe this could be automated as well. Theoretically, each shell in a salvo would have identical fuze timing to maximize the lethality of the bursts.

[pgollin]

Another option is to consult contemporary archival documents (PiNGs for example), ...........

.

That is an interesting acronym I haven't come across before, could you tell me what it stands for and the reference of where they are available,

Thanks.

.

[Byron Angel]

That is an interesting acronym I haven't come across before, could you tell me what it stands for and the reference of where they are available,
Thanks.

..... Sorry about that, Phil. Especially as I rail on endlessly that rampant use of acronyms is a portent of the end of Western civilization.

PiNG = "Progress in Naval Gunnery". Several editions can be found on the web in the reference archive of the HMS Hood Association/RN Admirals website.

B