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Old 06-02-2016, 01:41 AM   #1
Tallor
 
Join Date: May 2016
Default WWII: 40mm Autocannon VS tanks?

I was watching a bit of War Thunder and one of the "epic plays" was a 40mm anti-aircraft gun taking up the role of "tank destroyer".

It got me thinking: Is this even remotely possible? According to ol' 3rd Edition's WWII core book, the 40mm does 6dx6(0.5) pi++ plus 3d crushing explosion and [4d] cutting fragmentation. That (0.5) modifier is going to make its average damage of 126 a lot less potent... but does this 40-mil still have a chance against lighter tanks, or even older, heavy tanks with spalling issues?

What do you think?
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Old 06-02-2016, 01:48 AM   #2
Tallor
 
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Default Re: WWII: 40mm Autocannon VS tanks?

Note: This is assuming that both A) The AA Gun isn't under direct tank gun fire, of course, and B) The AA Gun gunner is a remarkable shot!
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Old 06-02-2016, 02:03 AM   #3
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Default Re: WWII: 40mm Autocannon VS tanks?

I think Warthunder assumes that they are firing AP ammo, like the Brittish 2 pounders that were also 40mm fired. The 2 pounder was fairly ok anti armor weapon early on in the war, so a 40mm autocannon would likely be too with AP ammo.

With saphe ammo: Not really useful unless you get flanking shots against lighter tanks or facing something like an armored car or the equivalent(pz1).

Later in the war: not useful against anything called a tank even with AP.
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Old 06-02-2016, 02:06 AM   #4
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Default Re: WWII: 40mm Autocannon VS tanks?

Quote:
Originally Posted by Tallor View Post
I was watching a bit of War Thunder and one of the "epic plays" was a 40mm anti-aircraft gun taking up the role of "tank destroyer".

It got me thinking: Is this even remotely possible? According to ol' 3rd Edition's WWII core book, the 40mm does 6dx6(0.5) pi++ plus 3d crushing explosion and [4d] cutting fragmentation. That (0.5) modifier is going to make its average damage of 126 a lot less potent... but does this 40-mil still have a chance against lighter tanks, or even older, heavy tanks with spalling issues?

What do you think?
Its going to depend massively on what it's firing, that looks like a HE round so an anti-air round, so no good against all but the lightest ground vehicles.

What cannon is going to effect this:

The Vickers S (which was a plane cannon) had muzzle velocity of 570 m/s


The Bofors 40mm is faster but obviously bigger


The German's had a 37mm cannon which I think came out of the Flak 18/56 the closest in High tech to that is I think the Rheinmetall 3.7cm PaK, written up in pg 140. (But if anything the other cannon will be better with a higher muzzle velocity etc).


Thing is these stopped being ground based anti tank guns early in WW2 as tank armour got thicker.

But planes using lighter anti tank cannon was very much a thing in WW2 as they fired down through the much thinner roof/deck armour.

That Rheinmetall 3.7cm PaK, has a APEX round that is (Dmg 7dx4(2) pi++). with a 2d [2d] cr ex follow up

This will happily go through the Turret roof DRs 55 & 70, and Deck DRs of 30 & 50 of the Panzer 4 & Sherman, but not so much the DR 280 & 220 of the front of both (it's closer for the Sherman though)

Edit: it will go through the sides as well

Last edited by Tomsdad; 06-03-2016 at 01:35 AM.
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Old 06-02-2016, 02:15 AM   #5
Tallor
 
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Default Re: WWII: 40mm Autocannon VS tanks?

Quote:
Originally Posted by weby View Post
I think Warthunder assumes that they are firing AP ammo, like the Brittish 2 pounders that were also 40mm fired. The 2 pounder was fairly ok anti armor weapon early on in the war, so a 40mm autocannon would likely be too with AP ammo.

With saphe ammo: Not really useful unless you get flanking shots against lighter tanks or facing something like an armored car or the equivalent(pz1).

Later in the war: not useful against anything called a tank even with AP.
Would an AA gun really use AP ammo, though? Assuming it was loaded up to fight aircraft.
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Old 06-02-2016, 02:18 AM   #6
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Default Re: WWII: 40mm Autocannon VS tanks?

Quote:
Originally Posted by Tomsdad View Post
Its going to depend massively on what it's firing, that looks like a HE round so an anti-air round, so no good against all but the lightest ground vehicles.

What cannon is going to effect this:

The Vickers S (which was a plane cannon) had muzzle velocity of 570 m/s


The Bofors 40mm is faster but obviously bigger


The German's had a 37mm cannon which I think came out of the Flak 18/56 the closest in High tech to that is I think the Rheinmetall 3.7cm PaK, written up in pg 140. (But if anything the other cannon will better with higher muzzle velocity etc).


Thing is these stopped being ground based anti tank guns early in WW2 as tank armour got thicker.

But planes using lighter anti tank cannon was very much a thing in WW2 as they fired down through the much thinner roof/deck armour.

That Rheinmetall 3.7cm PaK, has a APEX round that is (Dmg 7dx4(2) pi++). with a 2d [2d] cr ex follow up

This will happily go through the Turret roof DRs of 55 & 70 for the Panzer 4 & Sherman, but not so much the DR 280 & 220 of the front of both (it's closer for the Sherman though)
So if I invent parking garages, then drive the AA gun up a parking garage, and fire downwards, I might destroy a WWII tank with WWII AA technology? :P
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Old 06-02-2016, 02:33 AM   #7
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Default Re: WWII: 40mm Autocannon VS tanks?

Quote:
Originally Posted by Tallor View Post
Would an AA gun really use AP ammo, though? Assuming it was loaded up to fight aircraft.
Many smaller AA guns have used API as main AA round, as smaller bursting shells were both unreliable and of questionable use. 40mm was abut the lowest with reliable bursting shells at WWII.

Loaded? The Bofors gun was mostly top hopper loaded with clips, so inserting an API clip if you had them available would be fast and then you would have API loaded few second later..

But historically, yes SAPHE was the normal load due to being most effective against soft skinned targets like airplanes, but if you planned to use it secondarily as AT gun like in Warthunder, you would likely field also API(that is still useful against aircraft, just not as good as the SAPHE)
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Old 06-02-2016, 02:54 AM   #8
Tallor
 
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Default Re: WWII: 40mm Autocannon VS tanks?

Quote:
Originally Posted by weby View Post
Many smaller AA guns have used API as main AA round, as smaller bursting shells were both unreliable and of questionable use. 40mm was abut the lowest with reliable bursting shells at WWII.

Loaded? The Bofors gun was mostly top hopper loaded with clips, so inserting an API clip if you had them available would be fast and then you would have API loaded few second later..

But historically, yes SAPHE was the normal load due to being most effective against soft skinned targets like airplanes, but if you planned to use it secondarily as AT gun like in Warthunder, you would likely field also API(that is still useful against aircraft, just not as good as the SAPHE)
SAPHE rounds have the explosiveness of HE, but don't have the fractional armor divisor, correct?
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Old 06-02-2016, 02:58 AM   #9
Ulzgoroth
 
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Default Re: WWII: 40mm Autocannon VS tanks?

40mm cannon could certainly be effective against a number of WWII armored vehicles, especially early in the war. That would be mainly when firing AP rounds, not the HE or HEC rounds often preferred for AA work, but perfectly serviceable in the same gun.

War Thunder, for those not aware, has ammo selection. Typically (once you've unlocked the options) any of the AA vehicles will be able to load all-explosive, all-AP, or a mix. In some cases an APHC option is available (and sometimes preferable against aircraft as well as tanks, because faster rounds mean less leading the target).
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Old 06-02-2016, 03:03 AM   #10
Calvin
 
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Default Re: WWII: 40mm Autocannon VS tanks?

As a player of Warthunder I can say that the game gives a lot of ammo options. Even with AA vehicles you can select ammo usually designed for AT rather than AA work. In that particular clip the cannons were likely using pure AP or API rounds. I think the game designers are aware that players will use things in ways for which they were never intended.
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