Nato guns :20 Pdr. - 90 mm and 105 mm

Looking at Nato tanks in 1950-1970 I wonder why the U.S stuck to the 90 mm firing HVAP and HEAT for so long in their M47 and M48 MBT.

Compared to the britsh 20 pdr. firing APDS and HESH it seems to be a bit mediocre gun, and abslutly inferior to the british 105 mm which later replaced it.

My questions are :

- Could the 20 pdr ad 90 mm guns be considered adequate against cntemporary Soviet MBT ?

- How did the 90 mm used in the perform in Israli service ?

- What are the relative merits of these three guns in terms of accurasy, armor penetration and general purpose usage (HE etc) ?

 

I have absolutely no data, but when I was a tanker, the M60 had just come into service. Thus, there were still a lot of M48 variants around, and sergeants who had served in M48's. Most of these NCO's (as old timers are wont to do) complained that the M68 105 mm was not nearly as accurate as the 90 mm. Who knows? I do know that at 1200 m we could hit 2" x 4" stakes with the 105 mm HEAT-TPT more times than not.

 

Just found this on the TDI (The Dupuy Institute) site,

Full text at http://www.dupuyinstitute.org/ubb/Forum ... 00016.html
I don't know why the US stuck to the 90, when it was just about comparable to the 17 pr, but NIH syndrome might have been involved :lol:
I haven't done any calculations re these guns and modern Russian MBTs but I would imagine they'd be decidedly iffy at "normal" combat ranges. Short answer would be that if they were adequate then why were they replaced? I would guess that they both became marginal somewhere/ somewhen about the time the L7 105 came into service (or probably before that, given dithering by governments). Likewise the 105 is hardly regarded as a serious threat to modern MBTs, hence the switch to 120mm, of ever-increasing calibre length and V0: ~about 1600-1800 metres/sec these days, with 15:1 or greater L/D APFSDS

 

Please humour a poor pleb - what does NIH stand for?

I was always a little surprised that the original M1 Abrahms had only a 105mm, especialy as the UK had been using 120mm on Chieftains since the 1960s.

Ah well, they've caught up now.

 

There's far more to penatrative ability than just the width of the barrel.

Firstly the length is just as important. Secondly the type of shell being used. Also velocity has no bearing on the ability of HEAT charges to penetrate. That's why PIAT's worked of just a spring! Velocity is often better achieved from longer barrels than "bigger" guns.

It might just be that the US had a reasonable penetration with the 90 mm and therefore had no reason to upgrade at the time.

FNG

 

I understand that caliber does not equal ability, but AFAIK the 90mm & 105mm were 'fairly' inferior to other guns around at the time.

Although, as ever, I am happy to be shown statistics that prove me wrong.
And, as ever, I suspect they do exist!

 

It's just that you can't compare a guns effectivness just be looking at it's size.

I've no idea how good or bad the 90mm was.

FNG

 

Phip wrote:
'Thus, there were still a lot of M48 variants around, and sergeants who had served in M48's. Most of these NCO's (as old timers are wont to do) complained that the M68 105 mm was not nearly as accurate as the 90 mm.'

This is a bit surprising, the L7 105 mm has always been considered a very accurate gun, but could the answer be that the L7 was more or less optimized for firing hyper velocity APDS rounds instead of HE/HEAT rounds?

Ricky wrote :
'but AFAIK the 90mm & 105mm were 'fairly' inferior to other guns around at the time. '
Which guns do you mean ?
I know the 120 mm guns were more powerful than the L7 105 mm,
But on the other hand, the L7 105 mm did prove it worth in various battles.

I agree with FNG, he US must have considered the 90 mm suffeicent and it might have been a better all-roud weapon than the 20 pdr, but it is surely very much inferior to the L7 105 mm which did replace both guns.

Does anybody have any hard facts regarding the prefoamce of these three tank guns ?
I have gotten the understanding, that when it comes to anti tank warfare the 90 mm were more or less equal to the 17 pdr , the 20 pdr more or less equal to the 88m L71 and the 105 mm about 25 % more powerfull than the 20 pdr.
But when it comes to accuracy and general performance I have no ideas whatsoever.

 

Sorry -
the US tank guns vs the British (and rest of NATO)

I agree - we need some hard stats before we can actually get anywhere. Tony? Christian?

 

Now, here is what I can glean from the net...
I'll see if my books have anything better.

The Chieftain used the Royal Ordnance 120mm L11A5 gun.

here:
http://www.janes.com/defence/news/jdw/j ... _4_n.shtml

says:
“APDS L15 The APDS round was the original anti-armour element of the 120 mm L11 series tank gun ammunition family. While it has been largely replaced as the primary anti-armour round by APFSDS rounds the APDS L15 remains a potent armour-piercing munition with a high hit probability at combat ranges; it has been estimated that the APDS L15 can penetrate 355 mm of armour at 1,000 m. The subprojectile is stated to be capable of penetrating the armour of most current MBTs at battle ranges. The APDS L15 uses a dense tungsten alloy penetrator subprojectile carried in a light alloy sabot. The projectile assembly is fired using the L4 CCC which contains 8.4 kg of NQ/S53-12 propellant. Muzzle velocity is 1,370 m/s.”

The M47/48 used the M36 90mm gun - no stats found.

The M60 used the M68 105mm gun, which was a modified British L7 weapon (modification as far as I can tell involved a different type of breech being installed). Again, no stats found.

The obvious question to me is if the L7 was as good/better as the L11, why did the Chieftain bother with the L11?

 

NIH = Not Invented Here

see also NOT syndrome.
NOT = Not Our Technology

 

Thanks Notmi

 

From 'M48' Modern Combat vehicles 4 Geoffrey Tiloltson

Quote :
About the 90 mm gun
'While the 20 pdr gun ofthe Centurion was superior to the 90 mm gun of the M46' page 11

'It had been intended that the Uk 20 pdr gun should be trialled in the M47 and it was hoped that the UK would test the T119. in the Centurion Mk3, It does not appear that this interchange ever took place' Page 13

'For a long time the US where quite satisfied with HVAP and no effort where made to produce APDS.
Although some APDS rounds were developed in 90 mm, None where standardised' Page 39

'The M48 where basically evenly matched with the T-34/85, But the 100 m gun of the T54 would probably be superior at ranges greater than 1.000 yd. This disadvantage might have been redressed by the higher hit probability afforded by the M48 phase IV fire control system. The M48 could defeat the armour of the T34 with ease up to 2.000 yd, but even the T34 presented a serious threat to the frontal armour of the M48 at up to 500 yd.' Page 41-42

'That the medium gun tank should be capable of defeating 4 in of armour angled at 60 deg. at 2.000 yd using kinetic enegery ammunitio, and the 90 mm gun M41 could not achieve this performance.' Page 101

 

Hi Cometfan - nice quotes thanks, but where are they from?

 

Hi Ricky

The quotes are from :
'M48' Modern Combat vehicles 4 By Geoffrey Tilloltson

I did state that in the subject, but I understand why you have overlooked that info

 

Well, nobody here really read those subjects in replies because those are usually blank.

 

Here's what I have about the various guns. The whole story isn't there (because of missing data). The E0 (muzzle energy is easy enough to work out, 1/2 MV^2/G, but the fact that 20 pr and 105 use APDS is probably more telling - HVAP (AFAIK it's the US term for APCR - correct me if I'm wrong) means that
A) the US round degrades in velocity more rapidly and
B) the impact energy loading (ie impact energy divided by shot area) is worse due to the extra diameter of the APCR - full calibre as opposed to sub-calibre.
All else being equal penetration equates roughly to impact energy loading
Partial Data
Gun Calibre V0 Ammo L/ Proj Wt
20 pr Mk 1 83.4 1463 APDS 69
90 L/50 90 1250 APCR 50
M3A2 90 1021 APCR 52
M3 90 1021 APCR 52 7.62
M36 90 1167 APCR 52.5
T15E2 90 1143 APCR 7.58
L7A3 105 1470 APDS 51
V0 (muzzle velocity) in metres/ sec, Projectile weight in kilogrammes.

 

Hi Oli

Nice posting - I'll go looking for more information regarding the shell weights missing.
Fortunately we have a quite efficent public library system in Denmark, so Iit should be posible to find som useful info.

 

I'm trying (and have been for deacades) to get an excel package done listing ALL tank and AT guns with calibre, L/, V), shot/ shell weight, diameters etc. I will post it somewhere (possibly on my own website) and ask members to add/ confirm data.
Then we'll all be singing from the same hymn sheet...