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Old 06-03-2016, 08:05 AM   #41
Tomsdad
 
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Default Re: WWII: 40mm Autocannon VS tanks?

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Originally Posted by Ulzgoroth View Post
Interesting observation, though. If I try to stat more WWII armor at some point I'll need to think about how to factor it in.
Yeah Sloping and metal quality

Roll on Vehicle design!

Actually a system like the armour articles would work, DR per inch, WM, adjustment mods for different slopes (as opposed to different construction types) etc., etc

Surface area would be more complicated though, (and would have several factors including slopping)
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Old 06-03-2016, 08:49 AM   #42
borithan
 
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Default Re: WWII: 40mm Autocannon VS tanks?

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Originally Posted by Ulzgoroth View Post
...you should maybe note that the British 2 pdr tank gun is 40mm. And of course there was the American 37mm. Neither compare favorably to later, larger caliber high velocity guns, of course, but both worked quite well against early-war tanks.

Of course if they were using anti-aircraft HE shells rather than some flavor of AP, you should expect them to have terrible results even against downright terrible tanks.
Oh, I know the 2 pdr was 40mm. And yes, I presume the Bofors guns were using HE, but it seems odd that the British didn't ever seem to consider using the weapon in an anti-tank capacity more often if the only issue was using the appropriate ammunition. The Germans were very happy using anti-aircraft weapons against ground targets. I don't know if they even had an AP round issued. I guess with the Pacific theatre getting lower priority and probably expecting little armour they might not have been issued any even if it was available.

Apparently the Hungarians had their own AP shell for the Bofors gun with penetration which seems to be similar to the 2 pdr. However by the time it was being used on the Eastern Front it was very underpowered vs Russian medium tanks.
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Old 06-03-2016, 11:51 AM   #43
Tomsdad
 
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Default Re: WWII: 40mm Autocannon VS tanks?

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Originally Posted by borithan View Post
Oh, I know the 2 pdr was 40mm. And yes, I presume the Bofors guns were using HE, but it seems odd that the British didn't ever seem to consider using the weapon in an anti-tank capacity more often if the only issue was using the appropriate ammunition.

....
Well as stated they didn't need to as they had the 2lb cannon anyway.

Another factor is a 40mm bofors gun and carriage is almost 6,000lbs. Now some of which is due to it being an anti-air platform, but some of it is to do with it's to do with the firing mechanism that can accommodate a much faster Rof (6x that of the 2lb cannon)


If you look at similar calibre dedicated anti tank guns at the time, that are far smaller and lighter*. A big part of being an anti tank gun is being quick and easy to move and hide. (Especially if you're a 40mm gun who has to rely in short range shot placement on weak spots)

Don't get me wrong I'm sure Bofors guns were used in anti tank roles when the need arose. But ultimately to make it a dedicated anti tank gun you'd end up changing it so much you might as well just use the 2lb gun anyway.


Anti tank guns of such calibre were obsolete pretty quickly in all but the pacific theatre, and that was a theatre where you wouldn't fancy dragging a heavy anti tank gun around in (and as above you won't need to anyway).

In Europe / North Africa if you going to move a heavy anti tank gun around your going to go with a 17lb gun which can tackle most tanks you're likely to meet.




*some comparisons the British 2lb is heavy and big in this class at 1795 lbs, the German Pak 37 was 990lbs, the US M2 is 912lbs.

Last edited by Tomsdad; 06-03-2016 at 12:29 PM.
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Old 06-03-2016, 12:52 PM   #44
johndallman
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Default Re: WWII: 40mm Autocannon VS tanks?

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Originally Posted by Tomsdad View Post
WAnother factor is a 40mm bofors gun and carriage is almost 6,000lbs.

In Europe / North Africa if you going to move a heavy anti tank gun around your going to go with a 17lb gun which can tackle most tanks you're likely to meet.

*some comparisons the British 2lb is heavy and big in this class at 1795 lbs, the German Pak 37 was 990lbs, the US M2 is 912lbs.
The 17-pounder is slightly heavier than the Bofors. The 6-pounder is only 2,520lbs, by far the best value for weight if it will do the job. Having taken a good look at the 17-pounder at Woolwich, it's really big and cumbersome.
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Old 06-03-2016, 02:31 PM   #45
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Default Re: WWII: 40mm Autocannon VS tanks?

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The 17-pounder is slightly heavier than the Bofors. The 6-pounder is only 2,520lbs, by far the best value for weight if it will do the job. Having taken a good look at the 17-pounder at Woolwich, it's really big and cumbersome.
IIRC it also had a beast of a recoil - that being why British tank designers stepped back down to the 77mm gun. The 17lbr's first outing was the "Pheasant" project - with the gun mounted on a 25lbr howitzer carriage. The recoil, apparently, was excessive and tended to break the carriage.
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Old 06-03-2016, 07:58 PM   #46
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Default Re: WWII: 40mm Autocannon VS tanks?

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Originally Posted by Tomsdad View Post
Yeah Sloping and metal quality

Roll on Vehicle design!

Actually a system like the armour articles would work, DR per inch, WM, adjustment mods for different slopes (as opposed to different construction types) etc., etc

Surface area would be more complicated though, (and would have several factors including slopping)
For real tanks with good data, you don't need any sort of system. Just the design information on armor thickness and slope, trivial trigonometry, and a clear idea of what DR/mm to use for the material.
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Old 06-04-2016, 01:40 AM   #47
Tomsdad
 
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Default Re: WWII: 40mm Autocannon VS tanks?

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Originally Posted by johndallman View Post
The 17-pounder is slightly heavier than the Bofors. The 6-pounder is only 2,520lbs, by far the best value for weight if it will do the job. Having taken a good look at the 17-pounder at Woolwich, it's really big and cumbersome.
That was kind of my point, if you going to have a big cumbersome anti-tank gun in Europe your going to go for the 17lb gun that will take out pretty much anything on the field than a fast firing 40mm bofors which is much more likely to be ineffective but still with all the issues of being big and cumbersome. i.e all the issues none of the benefit.

In arenas where you don't need such a powerful gun you can avoid lugging a big cumbersome gun around and still have the power of the 40mm with a 2lb gun and a lot less weight

The problem with the 6lb gun is that it was pretty borderline ineffective even when it was introduced, and it only got worse from there. But yes still a good step up from the 2lb for not a lot more weight (the British 2lb was very heavy for it's class though)

But yeah the 17lb is a big heavy gun, but as you say only slightly heavier then the a 40mm Bofors anti air platform. So even if you can shave some weight and size of such platform for dedicated anti-tank use, your still going to be compromising. The problem is you compromising in one direction (increased weight etc) but not getting a pay off in the other, a 40mm is limited in effectiveness vs. thicker armour.

Now to be fair you use different guns in different sets up in different ways here. A 40mm bofors anti air gun is firing at 120 rpm, because it's job is to chuck as much stuff at distant fleeting targets as possible, were even a glancing HE hit will possibly do the job. So you have all the infrastructure to enable fast firing and a whole load of ammunition to burn though.

Anti tank fire is pretty much the opposite, that's all about about either you out-ranging the tank (which you won't be doing with a 40mm unless it's a very early tank), or taking a a few aimed shots at the right time before you are found and blown to pieces.

Quote:
Originally Posted by Ulzgoroth View Post
For real tanks with good data, you don't need any sort of system. Just the design information on armor thickness and slope, trivial trigonometry, and a clear idea of what DR/mm to use for the material.

True, but it's the latter I think that's the issue, as a lot of listing don't rate the value of such material by standard that can be used in GURPS. Although more recent tanks with more exotic armours do occasionally give an equivalent in thickness vs. different damage Ke/HEAT I've noticed i.e RHAe)

Last edited by Tomsdad; 06-04-2016 at 01:44 AM.
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Old 06-04-2016, 02:30 AM   #48
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Default Re: WWII: 40mm Autocannon VS tanks?

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The problem with the 6lb gun is that it was pretty borderline ineffective even when it was introduced, and it only got worse from there. But yes still a good step up from the 2lb for not a lot more weight (the British 2lb was very heavy for it's class though)
I thought the 6-pounder was very respectable...as an anti-tank gun. Where it came up short was as an infantry support gun, because its HE was no match for what you could get out of a 75mm gun.
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Old 06-04-2016, 04:42 AM   #49
Tomsdad
 
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Default Re: WWII: 40mm Autocannon VS tanks?

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Originally Posted by Ulzgoroth View Post
I thought the 6-pounder was very respectable...as an anti-tank gun. Where it came up short was as an infantry support gun, because its HE was no match for what you could get out of a 75mm gun.
Oh it's a fine gun in it's class, but remember it's sort half way between a 50mm and a 75mm. 50mm is pretty much the first half of the war, being replaced by 75mm+ later on

Even when firing AP it didn't fire it at particularly high velocity, so it had to be pretty close to beat say a panzer 4's front armour, and that causes problem for using the gun in combat for several reasons.


It absolutely rocked the first half of the war against P1-3 and early P4's, but ended up effectively out ranged the later it got.

Look at the difference in penetration ability between the 6lb QF

and the german 75mm,


Yes the 6lb can just about get through the front of P4 but it's close (and that's at 100m), but look at the other gun's performance at similar and longer ranges.

Now yes the German gun is 75mm and more powerful etc, etc but it's only 25% heavier.



And yeah you are right about the HE being a bit lacklustre out of a smaller calibre. (but then that what your 25lb howitzers are for I guess)

Last edited by Tomsdad; 06-04-2016 at 10:40 AM. Reason: took the soviet gun out as the pentration table is likley wonky
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