Fire Control, Ranging, Dispersion

[Stuart Galbraith]

Yeah got my eye on the B36 one too.

The books on Centurion Challenger 1 and Challenger 2 are all good. The one on C2 probably ranks as the best out there.

[Gorka L. Martinez-Mezo]

On 2/18/2021 at 7:11 PM, Stuart Galbraith said:

Ive got a nagging feeling there was a WW2 combat aircraft (or perhaps even pre ww2) that had MG's to assist with aiming heavier armament, but im damned if I can recall which one. P39?

The Hurricanes armed with the 40mm Vickers S aerial gun used 7,7mm Brownings to get the range before firing the large cannons

[Stuart Galbraith]

You know, I think you have it. I didn't consider the possibility of a ground attack aircraft. Well done.

[JWB]

5 hours ago, Gorka L. Martinez-Mezo said:

The Hurricanes armed with the 40mm Vickers S aerial gun used 7,7mm Brownings to get the range before firing the large cannons

https://weaponsandwarfare.com/2017/04/13/hurricanes-with-vickers-class-s-40mm-gun/

[KV7]

On 2/9/2021 at 10:23 PM, Gorka L. Martinez-Mezo said:

Apparently the Soviets criticized HESH due to the lack of fragmentation by itself and fuzing problems against sloped targets. A HE round as used by mostly everybody else appears to be a better infantry support shell than HESH although without secondary AT capability.

Soviet/Russian tests and doctrine seem to indicate that HE is and is considered just as good or even superior vs armor. Where HESH is going to be effective vs modern armor (i.e vs relatively thin monolithic armour as on hull sides, and the turret and hull roof, some glacis such as on the M1 etc.) 125mm HE on delay is likely going to penetrate the armor, or at high angles of incidence vs thin plate, the HE is going to break it if it fuses. And against areas which are resistant, i.e. the turret front, you are only getting secondary damage to other areas from fragments and blast, and here the HE is better. Against AFV with medium armour, e.g most IFV, HE is far superior because HE on delay will penetrate and explode internally,  almost certainly causing a total kill, whereas HESH is doing to do damage only from scabbing, and even here the various anti-HEAT add-on armor may be enough to stop that. 


 

[Stuart Galbraith]

The whole point of HESH today is not to kill modern armour. its been outmoded at that since the T64A made an appearance. Id argue the reason why its lingered is that it has a utility as an indirect round, its good at wall busting, and if it comes to it, is good at killing light or aging armour as well. Undoubtedly there are some modern HE rounds that can probably do all that as well, but I dont believe it was quite that simple in the 1960's when the L11 was introduced, or that simple in 1989/1990 when the Challenger 2 was designed.

Its a bit like the Gloster Gladiator. Yes, it looks ridiculous people were still using that in WW2. OTOH, the lead up to WW2, it was quite logical someone was going to build it, and as it turned out, it did have some advantages everyone overlooks when clearly a monoplane was the future.

Its the difference between obsolete and obsolescence.

[KV7]

I don't think this can be the explanation, because variable fused HE is ancient, and even when the UK developed new ammunition for the FV433 including a larger and higher capacity HE round (L31) the intention was that the loadout would still include 6 HESH, which is notable because that significantly reduced the indirect fire capability of what is, after all, self propelled artillery, without it gaining any appreciable anti-vehicle capability.

I think the simplest explanation is that there was some internal norm created where HESH was considered the best way to get a dual use round, and that persisted after it was no longer plausible.

If the UK wanted some class of dual use rounds for use by things like FV433 and the FV101, it would have been better to develop some HEAT-FRAG round. This is especially the case for the 76mm L23 because the 76mm  HESH round was too small to be good for anything, whereas a HEAT round would be a threat to the T-55 even from the front, and with a suitable fragmenting casing would have been superior vs infantry.

If you really wanted to have the option to use FV433 or similar as an assault gun vs bunkers and reinforced buildings, then it would have made sense to develop a concrete piercing APHE round. With the super charge it would have had a useful penetration and far better terminal effects, especially as plain old reinforced concrete with sandbagging or tamped earth on the rear face (of the sort we see everywhere in Syria) is quite resistant to HESH, as the sandbags/earthen berm/44 gallon drums full of debris will stop any concrete scabs.
 

[Stuart Galbraith]

14 minutes ago, KV7 said:

I don't think this can be the explanation, because variable fused HE is ancient, and even when the UK developed new ammunition for the FV433 including a larger and higher capacity HE round (L31) the intention was that the loadout would still include 6 HESH, which is notable because that significantly reduced the indirect fire capability of what is, after all, self propelled artillery, without it gaining any appreciable anti-vehicle capability.

I think the simplest explanation is that there was some internal norm created where HESH was considered the best way to get a dual use round, and that persisted after it was no longer plausible.

If the UK wanted some class of dual use rounds for use by things like FV433 and the FV101, it would have been better to develop some HEAT-FRAG round. This is especially the case for the 76mm L23 because the 76mm  HESH round was too small to be good for anything, whereas a HEAT round would be a threat to the T-55 even from the front, and with a suitable fragmenting casing would have been superior vs infantry.

If you really wanted to have the option to use FV433 or similar as an assault gun vs bunkers and reinforced buildings, then it would have made sense to develop a concrete piercing APHE round. With the super charge it would have had a useful penetration and far better terminal effects, especially as plain old reinforced concrete with sandbagging or tamped earth on the rear face (of the sort we see everywhere in Syria) is quite resistant to HESH, as the sandbags/earthen berm/44 gallon drums full of debris will stop any concrete scabs.
 

Id agree it was a norm at least up till the mid 1980's. After that, I dont think the British Army is quite as hidebound as people think. It fought the MOD to get TIS for Challenger 1 and Chieftain despite a lot of opposition from the MOD that would seemingly have been happy to stick with illumination rounds. As ive said before, the reason why it endured was because the envisaged the replacement would be L30. The reason why they stuck with L30 is because they wanted a gun replacement in Chieftain and Challenger. 

 

 If regunning with L30 been done at the beginning of the 1980's it would much more sense. That the program seems to have slipped and then only introduced in one tank long after the cold war make it looks very odd indeed. But the logic of the choice stands up, even if ultimately proved something of an achillies heel for Challenger 2.

Ive got a nagging feeling ive read somewhere of a Scorpion killing a T55 with a HESH round in 1991, but I wont swear to it.

[KV7]

I think it was an Iraqi license made T-62 actually, disabled by a Kuwaiti Scorpion. This is plausible as there are many areas which are vulnerable, especially as the shell is plunging somewhat even at modest range and so roof hits are possible.

But in comparison, less exceptional circumstances are required for a kill with say PG-15V. The Soviets had a similar problem though as 2A28 didn't even get a HE round till 1974.

Edited April 3, 2021 by KV7
spelling.

[bojan]

11 hours ago, KV7 said:

I think it was an Iraqi license made T-62 actually...

Iraq never did 62s, only assembled some T-72s.

 

Quote

disabled by a Kuwaiti Scorpion

Saladin IIRC, but same gun anyway. Odd things happen in the war, there was instance in the Yugoslav wars where BR-350B AP from PT-76 penetrated T-55 "from the front", but thing is that it was fired from a significant elevation and hit and penetrated TC hatch. I would not count on such things being any sort of regular, reason those are often remembered is that they generally happened once.

In both instances, if those hit front glacis or turret... there would be very little ill effects for the tank. Unlike 76mm HEAT that could easily penetrate both.

Edited April 3, 2021 by bojan

[KV7]

Yes HESH and HE can with rarity kill basically anything, if it fuses against some thin plate, and even some thin plate which will typically deflect APFSDS. But relying on such a mechanism is usually going to be suicidal or close to it.

[DougRichards]

On 2/20/2021 at 7:00 AM, Gorka L. Martinez-Mezo said:

The Hurricanes armed with the 40mm Vickers S aerial gun used 7,7mm Brownings to get the range before firing the large cannons

So did some fighters when attacking ships with 3" rockets in a dive, except firing the 20mm cannon also provided at least some FlaK suppression and damage by themselves against destroyer sized targets.  

[Wobbly Head]

On 2/11/2021 at 3:22 PM, Tim Sielbeck said:

Maintenance was a non issue.  In my four years I never saw a vehicle with a rangefinder issue and nobody that I talked to, who had been in much longer than I, ever mentioned a maintenance issue with them.

At short ranges, out to 1600m for SABOT and 1100m for HEAT, we were supposed to use the "battle sight" technique.  

  Maintenance is a non issue if you are not the one doing it. CR1 which was an upgraded Chieftain system even then all tanks would go through approximately 3 hours of testing with and adjusting with no faults before going to the range. The test equipment used was sensitive enough we had to stop the crews walking on the tank when it was parked and the engine off as it would affect these tests. 

For optical test we went with an error of half the MRS dot graticle  which using the rough formula error= Magnification of the sight x 2 error times the distance makes the error 10 magnification x 2 x .075 mills which gives you a +/-1.5 mill error

  The crews training and tests were in some cases the complete opposite of what we did as our tests were to find the errors but the crews were there to make their test consistent including any errors. So some of the crews were not understanding how our test were going to work but the cleaver ones just accepted them if we gave them a tank we had set up for firing instead of redoing the tests the way they were taught.

 One thing that was quite amusing is the commander bore sighting to a different target than the gunner is looking at was quite common it even happened to one tank crewed by the regimental gunnery instructor (commander) and squadron gunnery instructor(gunner). I let my Sargent tell them he could at least get a few  beers out of that  oops.

 

[Tim Sielbeck]

10 hours ago, Wobbly Head said:

  Maintenance is a non issue if you are not the one doing it.

 

The reason it was a non issue, with regards to optical range finders, is because nobody I talked to (or served with) had ever seen depot-level maintenance done on a range finder.  That doesn't mean we didn't check them before gunnery or during normal PMCSs.  It just means they were never an issue to be dealt with by higher maintenance.  Optical range finders in the M60 series were very robust systems.

[Stuart Galbraith]

But how would they deal with a near miss by 152mm artillery?

There is seemingly an underlying assumption that in war these systems would behave exactly as they would in peacetime. I remember reading about one of the atomic tests against an M48, and the tank basically was fine, lost some storage bins. But all the optics had to be replaced because they were damaged by flying debris. Now most tanks are going to have swap sights, but you are going to have a challenge replacing the optics on an optical rangefinder without a some extensive refitting.

Admittedly by that point whether your optical rangefinder worked or not was outmoded by the start of a nuclear war, it made a basic point to me. The more apertures, the more moving parts a system has, the more vulnerable its going to be in combat. The RMG had some basic accuracy issues, I can see that. When the shit started flying its going to be as .50 machine gun, which had demonstrated its basic reliability in numerous wars.

 

[DougRichards]

2 hours ago, Stuart Galbraith said:

But how would they deal with a near miss by 152mm artillery?

There is seemingly an underlying assumption that in war these systems would behave exactly as they would in peacetime. I remember reading about one of the atomic tests against an M48, and the tank basically was fine, lost some storage bins. But all the optics had to be replaced because they were damaged by flying debris. Now most tanks are going to have swap sights, but you are going to have a challenge replacing the optics on an optical rangefinder without a some extensive refitting.

Admittedly by that point whether your optical rangefinder worked or not was outmoded by the start of a nuclear war, it made a basic point to me. The more apertures, the more moving parts a system has, the more vulnerable its going to be in combat. The RMG had some basic accuracy issues, I can see that. When the shit started flying its going to be as .50 machine gun, which had demonstrated its basic reliability in numerous wars.

 

Depending on the war that you are fighting.  Sure on the plains of Northern Europe, the steppes, open desert, or dare I say it the prairie, you need a long range anti-armour rangefinder.

But to the Australian Centurion crews in VN (or their Matilda crew predecessors in Borneo and the like) long range fire control was not as useful as a co-ax firing tracer to put the main gun somewhere on target.  In VN crews would sometimes be using both the Browning .30 and the .50 ranging gun as co-ax against whatever targets were needed.  The main gun had mostly HE with a small number of AP, useful for pick and shovel work,  or for dealing with the very odd occasion when an RPG damaged the 20pdr and it had to be 'fixed' by firing an AP round to clear the bore, and remove about a quarter of the length of the barrel before continuing to fight with HE rounds (yes it happened).

[Wobbly Head]

11 hours ago, Tim Sielbeck said:

The reason it was a non issue, with regards to optical range finders, is because nobody I talked to (or served with) had ever seen depot-level maintenance done on a range finder.  That doesn't mean we didn't check them before gunnery or during normal PMCSs.  It just means they were never an issue to be dealt with by higher maintenance.  Optical range finders in the M60 series were very robust systems.

  A crew not seeing what actual work is involved is not uncommon. Sights by there very nature highly breakable glass on a front line vehicle so are designed to be easily replaced in anything from 2 minutes to about an hour for most British sights. Then they are shipped off to second line for repair. The sights mounts and linkages are designed and built for this. All most crews then see is when they report something broken the tech climbs on and an hour later their vehicle is now working. They don't realize that one of the major components has been changed and the damaged item is off to be repaired at a maintenance depot. The same goes for most items on a tank first line repair for techs is mainly box changing for the most part.

 The linkages and mounts can be changed in the vehicle and they do sometimes break which is rare but a large enough impact to throw off the linkages is also very likely to seriously damage the vehicle in some other way so in most cases it would be going to need overhauled at third line.

 

[Tim Sielbeck]

9 hours ago, Stuart Galbraith said:

But how would they deal with a near miss by 152mm artillery?

It depends on where the artillery round lands in relation to the forward view of the range finder and how far away it landed from the tank.  The openings on the rangefinder are fairly small and if the blast is not coming from the direct front the lenses will not be damaged.

 

9 hours ago, Stuart Galbraith said:

There is seemingly an underlying assumption that in war these systems would behave exactly as they would in peacetime. I remember reading about one of the atomic tests against an M48, and the tank basically was fine, lost some storage bins. But all the optics had to be replaced because they were damaged by flying debris. Now most tanks are going to have swap sights, but you are going to have a challenge replacing the optics on an optical rangefinder without a some extensive refitting.

A mechanical rangefinder would behave exactly in war as the did in peacetime UNTIL they took damage.  Optics would only be replaced if they were so scratched that it became very difficult to see through them.  Scratched lenses could be replaced when/if needed and, if I remember correctly, the lenses of the rangefinder were removable without removing the rangefinder body from the turret.  Until then there were other ways of determining range.

From TM 9-258: Elements of Optics and Application to Fire Control Instruments;

Auxiliary boresight (gun laying) reticle system.  The auxiliary boresight (gun laying) reticle system can be used for auxiliary sighting and range estimation if the left optical system becomes inoperative.  It can also be used to check range finder alinement by checking its coincidence with the left main boresight
reticle (16).  The system consists of two assemblies:  an auxiliary boresight (gun laying) reticle bracket assembly
and an auxiliary boresight (gun laying) lens assembly.

That M48 you mentioned probably had its turret turned towards the blast.  We were taught to turn the turret away from the blast for just that reason.  

9 hours ago, Stuart Galbraith said:

Admittedly by that point whether your optical rangefinder worked or not was outmoded by the start of a nuclear war...

No, that is not correct.

11 hours ago, Stuart Galbraith said:

The more apertures, the more moving parts a system has, the more vulnerable its going to be in combat. The RMG had some basic accuracy issues, I can see that. When the shit started flying its going to be as .50 machine gun, which had demonstrated its basic reliability in numerous wars.

There are more moving parts on an M2 .50 cal. that there is on a M17A1 Rangefinder.

[Tim Sielbeck]

1 hour ago, Wobbly Head said:

  A crew not seeing what actual work is involved is not uncommon...  All most crews then see is when they report something broken the tech climbs on and an hour later their vehicle is now working. They don't realize that one of the major components has been changed and the damaged item is off to be repaired at a maintenance depot. The same goes for most items on a tank first line repair for techs is mainly box changing for the most part.

I don't know how the British Army does things but when I served my tanks did not go anywhere that I did not know about.  If the turret or hull mechanic worked on our tanks we were with him until the work was done.  If the company level maintenance needed to work on it other than on the line the crew took it to where it needed to go to get the work done on it.  We stayed with it until the work was done for the day or until the problem was rectified, whichever was required (spent more than one night up until 04:00 to 05:00 waiting for them to release it to me).  The same happened at the Battalion level.  If it had to go higher than that we had to drive the tank to wherever it had to go, drop it off, then go get it once it was done.  WE knew what was going on with our tanks and why.

 

1 hour ago, Wobbly Head said:

Sights by there very nature highly breakable glass on a front line vehicle so are designed to be easily replaced in anything from 2 minutes to about an hour for most British sights...  The same goes for most items on a tank first line repair for techs is mainly box changing for the most part.

 The linkages and mounts can be changed in the vehicle and they do sometimes break which is rare but a large enough impact to throw off the linkages is also very likely to seriously damage the vehicle in some other way so in most cases it would be going to need overhauled at third line.

 

Different design philosophies from different eras of tanks.  Mechanical verses electronic.

Our sights were built of many parts but the important ones were the housing and the sight elbows.  Exterior window of the housing damaged?  Switch it out with the TC's housing in the cupola.  Takes ten minutes tops and is a crew service item.  If the reflecting mirror of the housing is alright you could probably get away with just removing the broken glass of the window.

Hardest one to fix would be the GAS.  Have to remove linkages and dismount it to get to the front lens.

 

Edited April 5, 2021 by Tim Sielbeck

[Wobbly Head]

I guess one of the biggest differences in the British system is the tanks are assigned to the squadron not individually apart from the crew equipment and the REME LAD (light aid detachment)  is part of the squadron and accompany  the squadron so even when the vehicles are being repaired at the squadron(company) level they have never left the squadron and have squadron personnel with them. So if the squadron leaders tank is down for repair he could take another tank from his squadron and leave the replacement crew with the tank being repaired to carry out other duties like guarding the LAD in war time or personal admin during range time. When not deployed as the LAD is part of the squadron the crews do not need to be present just someone to unlock the hatches or just assign the hatch padlock key as happens in most cases for any repairs to happen as the REME are squadron personnel . All the squadron commander is interested in is ready number which are supplied to him by the tiffy (Artificer Sargent SSGT in charge of the LAD)

 

The other big difference is the REME was much more broadly trained than the American system. if someone was a mechanic it covered the whole engine and running gear  and Instrument Techs (no longer a trade replaced by turret technicians) used to fix the sights which covered anything you can look through from a periscope to thermal sight and you could serve both first and second line repair. That meant the LAD were the company/Battalion  level support and if they couldn't get you moving they could be sending a replacement tank some repairs could be done second line but since most REME personal had done a stint in second line most knew if the repair was possible at second line.

 

 As for Mechanical verses Electronic I did my trade training on Chieftain Mk 12 and served with Challenger1 Mk 3 first line plus CVRT and Warrior and everything else with a sight. They were hardly advanced in the electronic department due to the MOD ducks ass spending philosophy. Thankfully I never had to replace a Chieftains gunners aux sight in the field as it was supposed to be one of the hardest dirtiest job to do due to them getting rusted and grimed in. The ones in the training tanks had been removed so often they practically fell out.

Edited April 5, 2021 by Wobbly Head

[DKTanker]

3 hours ago, Tim Sielbeck said:

 

Hardest one to fix would be the GAS.  Have to remove linkages and dismount it to get to the front lens.

 

Are you referring to the 105D?  A wedge bolt on the outside (3/8 or 7/6 hex head as I recall), two trunnion bolts (3/8 allen) and a push release pin for the hanger then slide it out.  No more than 10 minutes, easy peasy.  But yes, much more involved than the M32 or M36.  

If you lose the exterior glass to an artillery fragment et al,  to one of the RF end housing, it is quite likely that the mirror behind it is compromised as well.  So out comes the RF when time is available.  Still, depending on which end housing was hit the M17 could still be available as a direct fire sight.  As I recall the reticle was on the right side.

Say, Stuart, the M48 and M60s had three separate sets of optics for direct fire gunnery.  The gunner's primary sight was the periscope, and the telescope was his back up.  Also the rangefinder could be used by the TC to engage targets.  So if the gunner's periscope was knocked out there were still two sets of optics available.  The gunner could use his telescope or the TC could use the rangefinder.  So what about the Centurion?  When the gunner's periscope was knocked out did the loader pull the backplate and bolt out of the ranging MG and talk the gunner onto the target?  The world wonders.

[Tim Sielbeck]

Yes.  Having never had to remove it I always assumed it was more complicated than you have described.

[Stuart Galbraith]

13 hours ago, Tim Sielbeck said:

It depends on where the artillery round lands in relation to the forward view of the range finder and how far away it landed from the tank.  The openings on the rangefinder are fairly small and if the blast is not coming from the direct front the lenses will not be damaged.

 

A mechanical rangefinder would behave exactly in war as the did in peacetime UNTIL they took damage.  Optics would only be replaced if they were so scratched that it became very difficult to see through them.  Scratched lenses could be replaced when/if needed and, if I remember correctly, the lenses of the rangefinder were removable without removing the rangefinder body from the turret.  Until then there were other ways of determining range.

From TM 9-258: Elements of Optics and Application to Fire Control Instruments;

Auxiliary boresight (gun laying) reticle system.  The auxiliary boresight (gun laying) reticle system can be used for auxiliary sighting and range estimation if the left optical system becomes inoperative.  It can also be used to check range finder alinement by checking its coincidence with the left main boresight
reticle (16).  The system consists of two assemblies:  an auxiliary boresight (gun laying) reticle bracket assembly
and an auxiliary boresight (gun laying) lens assembly.

That M48 you mentioned probably had its turret turned towards the blast.  We were taught to turn the turret away from the blast for just that reason.  

No, that is not correct.

There are more moving parts on an M2 .50 cal. that there is on a M17A1 Rangefinder.

The only part that was exposed was the barrel, which they had a replacement for and was a relatively simple swap. I dont see anyone swapping the sight heads from an optical rangefinder with the same kind of alacrity outside of a rear area workshop.

And yes, there are alternatives to measuring range, absolutely, that wasnt my implication. My implication is an optical rangefinder is great at finding range, right up to the point when the vehicle starts taking hits. To be honest,yes, its somewhat unknowable how much of an issue it is, because the only people that seem to have used optical rangefinders on any scale in combat are the Iranians and Iraqi's, and they dont seem very forthcoming with their experience. But simple supposition leads me to think that a big metal tube that has lots of moving parts and takes up a large chunk of the turret, is probably going to be vulnerable to penetrating hits, probably even high explosive. Its got two exposed areas as opposed to one, its widthwise across the turret, and mounted at the very top of the turret where everyone and his uncle can fire rounds at it.  By contrast the RMG is mounted low down in the mantlet, is facing frontally so its going to be less vulnerable to  hits (and that did would likely jam the gun anyway), and its a system where you can pull the weapon out and remount one. Thats what, a half hour job tops?

 

 

 

 

[Stefan Kotsch]

As far as I know, the spare parts kit for every T-72 did not contain any spare parts for the end pieces of the rangefinder.  But, for the T-72 with TPD-K1 there was a replacement mirror head for each tank.  It was very easy to exchange, also for the crew.

However, a change was not enough.  Adjusting the laser was not so easy and, above all, not so quick to implement.  And the gun should always to be adjusted by shooting for different types of ammunition.  At least in theory.

Optical rangefinders are just too complicated and fragile systems.  This is work for the real specialists.

Edited April 6, 2021 by Stefan Kotsch
complement

[DougRichards]

9 hours ago, DKTanker said:

Say, Stuart, the M48 and M60s had three separate sets of optics for direct fire gunnery.  The gunner's primary sight was the periscope, and the telescope was his back up.  Also the rangefinder could be used by the TC to engage targets.  So if the gunner's periscope was knocked out there were still two sets of optics available.  The gunner could use his telescope or the TC could use the rangefinder.  So what about the Centurion?  When the gunner's periscope was knocked out did the loader pull the backplate and bolt out of the ranging MG and talk the gunner onto the target?  The world wonders.

You forgot looking straight down the barrel of the main gun....😀

What about using, in the right conditions, the spotlight as a targeting aid (almost suicidal I know 😬 ), or even using the normal co-ax?  Having another tank call out the range and bearing?