What prevented the QF 3.7-inch AA gun being used in the Anti Tank role.

[Urmel]

Time to post this again:

https://rommelsriposte.com/2010/04/27/g ... atilda-ii/

The Liddell-Hart figures are almost certainly the KwK38, since they refer to a document captured during BATTLEAXE (14 June 41).

[Don Juan]

Well the 5cm projectile had twice the mass of the 2-pdr, it also had a small bursting charge, which meant any after penetration damage was likely to be greater. Then it had a cap which made it less likely to shatter on hitting armour than the miserable 2-pdr shot.

Interestingly, the Ordnance Board did some testing on the effectiveness of the 5cm projectile's bursting charge, and found it to be not exactly reliable:

The cap only reduced the likelihood of shatter on face hardened armour, not on RHA, although it did reduce the tendency to ricochet on angled plates. It's notable that the initial muzzle velocity of the 5cm projectile when fired from the 5cm KwK 38 was only 2240 fps, in comparison to the 2600-2650 fps of the 2 pounder. However, the ballistic cap should have allowed it to better maintain its velocity in comparison to the uncapped 2 pounder AP shot.

[Don Juan]

Here's an interesting excerpt from AFV Technical Report No.2, written by my old mate William Blagden on 9th January 1942:

This reveals that there were two types of 5cm AP projectile used during Operation Crusader: an AP shell and an APC shell. I was puzzled by the fact that the Ordnance Board tests refer to 5cm APC while most sources refer to 5cm APCBC, and the anomaly seems to be because the cap was semi-ballistically shaped.

It appears that during Operation Crusader, most of the 5cm fired was AP, and I would guess that the APC superseded this projectile during early 1942. It is further clear that the captured German penetration figures refer to the AP shell, while the British figures generated during the Ordnance Board tests were using the APC shell - so they both refer to different types of ammunition.

The capped ammunition seems to have had a slightly reduced charge, although the semi-ballistic shape of the cap may have mitigated this by improving the flight characteristics.

[MarkN]

Here's an interesting excerpt from AFV Technical Report No.2, written by my old mate William Blagden on 9th January 1942:

This reveals that there were two types of 5cm AP projectile used during Operation Crusader: an AP shell and an APC shell. I was puzzled by the fact that the Ordnance Board tests refer to 5cm APC while most sources refer to 5cm APCBC, and the anomaly seems to be because the cap was semi-ballistically shaped.

I would concur with Blagden that (a) is 'shot' rather than 'shell' and is the equivalent of the British APHE 2-pdr round.
(c) is also more 'shot' than 'shell' since it uses mass and kinetic energy means to penetrate not chemical explosive effect. Calling it 'arrowhead' is a way to separate it from completely solid 'shot'. If the bakelite cap is designed for 'ballistic' purposes, as Blagden notes, then surely the round is more APBC than APC or APCBC? Mind you, if examiners of the ordnance are not entirely sure what the cap's purpose is, then the confusion is understandable. If the bakelite cap also has a 'contact adhesion' purpose, then APCBC seems reasonable.

[Gooner1]

Interestingly, the Ordnance Board did some testing on the effectiveness of the 5cm projectile's bursting charge, and found it to be not exactly reliable:

The cap only reduced the likelihood of shatter on face hardened armour, not on RHA, although it did reduce the tendency to ricochet on angled plates. It's notable that the initial muzzle velocity of the 5cm projectile when fired from the 5cm KwK 38 was only 2240 fps, in comparison to the 2600-2650 fps of the 2 pounder. However, the ballistic cap should have allowed it to better maintain its velocity in comparison to the uncapped 2 pounder AP shot.

The British were not really swung on the idea of a bursting charge, figuring, probably correctly, that most of the damage caused was by the kinetic energy of the projectile.

UK tests on a PzIII H gave a Brinell value of 500-600 for the front nose pate, 600-800 for additional plates, drivers front plate was 500-550, additional plates 600 and turret front of 400-500. So the tank had very 'hard' armour, ideal for breaking up uncapped projectiles.

[Gooner1]

Calling it 'arrowhead' is a way to separate it from completely solid 'shot'.

The 'arrowhead' must be the German PzGr40 round, what the British would call APCR.

[MarkN]

The British were not really swung on the idea of a bursting charge, figuring, probably correctly, that most of the damage caused was by the kinetic energy of the projectile.

Somewhere on my HD I have just such an analysis.

2RTR did a test shoot in February 1941 against Italian M.13 manned by sandbags to compare the capabilities and effects of AP and APHE. The results were similar. The 'key' difference was that by taking away some of the mass by inserting an HE bursting charge, the penetration qualities were reduced. It was assumed that the advantage of the 'killing effect' of the bursting charge was not great enough to offset the loss in penetration capability.

The 'arrowhead' must be the German PzGr40 round, what the British would call APCR.

That's how I see it too.

[Don Juan]

Here's another excerpt from Liddell-Hart's letter to Colonel Cooper:

The most interesting point here is on the brittleness of the additional 30mm plates on the Panzer III Ausf. H. This was observed during tests conducted in the UK starting with Armour Trial AT 37, in which the additional frontal plates were totally fractured by only four 2 pounder rounds. There is a somewhat painful thread about this very trial here.

What is significant in AT 37 is that the 2 pounder rounds were smashed on contact with the plates, and it is now clear that the over-hardness of the plates had the dual effect of smashing the 2 pounder rounds and smashing the plates themselves. What this also indicates is that the additional protection on the hull front of the Ausf. H was somewhat temporary in nature - exposure to sustained fire would soon see these plates broken off. The way the Germans appear to have used their tanks during Operation Crusader seems to indicate that they themselves were not hugely confident of their impregnability. They only attacked when they had overwhelming numbers, and otherwise used their tanks to lure the British tanks onto their anti-tank guns.

[MarkN]

The way the Germans appear to have used their tanks during Operation Crusader seems to indicate that they themselves were not hugely confident of their impregnability. They only attacked when they had overwhelming numbers, and otherwise used their tanks to lure the British tanks onto their anti-tank guns.

Don Juan,

You have taken the time to show the evidence that, even after the failure at Gazala, British institutional thinking based upon research and testing (not emotional complaining and whining) was that the 2-pdr with AP was only marginally less effective than the 5cm Pak38 or KwK L/42. The difference which opened up from Gazala onwards was du to the new face-hardened plate fitted to German pantsers - but not fitted to British pantsers. An issue that affected both the 2-pdr AND the newly introduces 6-pdr - albeit to a lesser extent.

At the same time, evidence shows that even as early as 1940, but throughout 1941, German battlefield success was achieved with Pak36, Pak38 and KwK L/42 at the expense of opposing 2-pdr armed forces. Capaibility was broadly similar. The outcomes were based upon how the equipment was used.

Which brings us full circle to the TO's original post. The 3.7" HAA gun was not reroled as an ATk gun during the timeframe he presents for 3 principle reasons:
1) There were no spare guns that could be afforded to be taken off HAA duty.
2) Even if there were spare HAA, the (lack of) mobility of the 3.7" gun was such that it was not deemed suitable for front-line deployment.
3) Even if there were spare 3.7" HAA guns and it had decent mobility, institutionally the British did not perceive a issue with the equipment they already had. And why should they?

Repeating, again, the quote...

In an acerbic vein, Bidwell and Graham commented, “In any case even if the guns [3.7-inch] had been made available it is doubtful if the desert commanders would have used them correctly, in view of the hash they made of the employment of all their own artillery.”

I'm not claiming anything new or revolutionary.

All this navel gazing to point blame here there and everywhere, and to Monday morning quarterback British victory, is post-event hindsight. Navel gazing mostly based upon historical falsehoods.
Nevertheless, it is true that in July 1942, an issue raised it's ugly head and questions were asked in the House. The issue was principally based around donkey walloper complaints not RA. They were post Gazala when 6-pdr ATk guns were already in the line and the some pantsers already had 75mm guns fitted. What the donkey wallopers were still having trouble coming to terms with was that they only way they could get a bigger gun into their British made tanks was to drop their rigid adherence to 3-man turrets.

[Don Juan]

I've actually just realised that armour trial AT 37 was against the front hull plates of the Pz.III Ausf.H (at 500+ Brinell) and not the additional plates, so even these were prone to shatter (although they also shattered the 2 pdr. rounds).

I'm starting to think now that the Matilda, Valentine, Crusader and Stuart were ALL better tanks than the Pz.III Ausf.H, and indeed that the British had better tanks available to them than the Axis forces from the beginning of the desert campaign right through to the end.

On the other hand, AT 37 does suggest the possibility that 30mm alone of 500 Brinell face hardened armour would keep out the 2 pounder at medium to long range, so this merits further investigation.

[Don Juan]

An armour trial was conducted on a Panzer III Ausf. H during March 1944, this being covered in Armour Trial Report AT 113. On this occasion the front nose plates held out against 2 pounder AP with aplomb. However, this does not mean the 2 pounder AP had no effect. Note the underlined portion:

From this description, it appears that the weld pads were removed by the final overmatching strike, but an examination of the test sheets shows otherwise:

This demonstrates that even non-penetrating hits can be deadly, and that it was worth firing 2 pounder AP at the hull front even if the strikes failed to penetrate. The slowest round to dislodge a weld pad was at 2266 fps, and although I don't have any ballistic curves for the 2 pounder, I would estimate that this corresponds to a range of 400 yards with standard 2 pounder ammunition (MV 2600-2650 fps) and 600 yards with HV 2 pounder (MV 2800-2850 fps). This would not be the longest range at which 2 pounder AP might be effective in dislodging the pads, just that these correspond to the lowest striking velocities used during the trial.

[Gooner1]

This demonstrates that even non-penetrating hits can be deadly, and that it was worth firing 2 pounder AP at the hull front even if the strikes failed to penetrate.

So it would be a better tactic for the British & co. gunners and tankers to open fire at longer range so they can 'wear down' the armour of the PzIII than to wait until they are at close range, where they'll probably have less opportunity to do so, I guess.

You can see why the Brits. were 'overclaiming' in their battles in this period too. They were visibly damaging the enemy only just not damaging them very much. I wonder if there are records for Panzer crew losses ..

[Don Juan]

So it would be a better tactic for the British & co. gunners and tankers to open fire at longer range so they can 'wear down' the armour of the PzIII than to wait until they are at close range, where they'll probably have less opportunity to do so, I guess.

You can see why the Brits. were 'overclaiming' in their battles in this period too. They were visibly damaging the enemy only just not damaging them very much. I wonder if there are records for Panzer crew losses ..

Dunno really. A lot of this depends on the vulnerability of the Pz.III Ausf. H front turret, which is a bit of a mystery at the moment, although I think 35mm was the max.

I know the German AT gunners were encouraged only to fire at the last moment. I think at this time the relative capabilities of the 2 pounder and 5cm Pak 38 and KwK 38 meant that there was a lot of metal flying around that wasn't causing a great deal of structural damage to tanks, so that most tanks knocked out were recoverable by whoever occupied the battlefield. One area where the British were more vulnerable was that up to and including Operation Crusader they didn't have armour protection on their ammo racks, so for a period their lighter tanks especially were much more vulnerable to brewing up than they ought to have been.

[Don Juan]

I've shown below on a very nice model the plating of the front turret of the Pz.III:

The purple is the front plate, which was 30mm RHA on both the Ausf. H and the Ausf. J (and probably also the Ausf. L and M). The British, in Armour Trial Report AT 113, reckoned that this plate was penetrable by 2 pounder AP from 1900 yards at 40 deg., but I think this is an overestimate, and 1600 yards at 30 deg. seems more realistic. As you can see there's not much target area to hit, so penetrating this plate would be more a matter of luck than judgement. The top and bottom runs of the plate are additionally protected by the mantlet depending on the elevation of the gun.

The yellow bit is one of the two trunnion blocks. I would guess that they would have been cast armour, probably 30mm thick on all versions of the Pz.III. Hitting these would not have penetrated the turret, but would impair or disable the elevation of the gun.

The blue part is the mantlet. I believe this would have been 30mm thick on the Ausf. H, and was definitely 50mm thick on the Ausf. J. Its shape suggests that it was cast armour, and therefore not face hardened. I don't think that you could shape face hardened armour in any form, and so it wasn't a simple job to place additional face hardened plates in this area. There would have been a certain amount of structure behind this mantlet, including vertical members, which may be why it is sometimes credited as being 35mm on the Ausf. H. There are small hatches for the loader and the gunner's sight, which look to have been perfect for dislodging. Otherwise it seems to have had a good ballistic shape.

The green portion is the front plate for the recoil cylinders. Again I think this would have been 30mm for the Ausf. H and was definitely 50mm. for the Ausf. J. This also appears prone to being dislodged, and Armour Trial Report AT 113 appears to confirm this. If this plate was penetrated, damage would have occurred to the recoil cylinders, likely disabling the gun. I would guess this plate was either cast or fabricated from RHA.

[MarkN]

I know the German AT gunners were encouraged only to fire at the last moment.

A couple of quotes lifted from 7 Armd Div Int Summs. First is from May, the second is from June 1941.

A shot from this gun [MarkNote: 50mm Pak38] at 50 yds range penetrated the front armour of our Mk.II "I" tank and lobbed inside, breaking the driver's ??? There was no splintering effect on the armour whatsoever.

It is not clear whether this was a British test shoot with a captured gun (unlikely) or the observations noted after the Brevity battle (likely). It also mentions that the Germans are using solid shot, when we know they didn't have any. This seems to suggest the bursting charge regularly didn't go off - a reliability problem that you have already highlighted.

During one action which caused heavy casualties to one of our sub-units the enemy concealed his guns and A/Tk guns among some tpt, ... and withheld fire until our tanks were within 300 yds.

This comes from the Battleaxe engagement. The context seems to be that waiting until 300 yds range before opening fire is not what the British were willing/prepared/doctrinally trained to do.

The same May Int Summ also provides guidance on the effectiveness of 2-pdr and encourages the gunners to go for the sides and rear (saying they are vulnerable even to small arms fire) but also says that hull and turret on Pz.III and IV can be engaged at 800 yds maximum successfully. It specifically mentions one Pz.III having been hit in the hull and set on fire at 900 yds range and at an angle to normal.

The tenor of the documents over a period of time encourages the British gunner (tank or ATk) to have a go at quite some distance and show some degree of bewilderment that the Germans deliberately hold their fire until much later.