Penetration and accuracy of lobbed weapons

Larry Holt · Post by **Larry Holt** » Tue Jul 10, 2001 8:02 pm

Originally posted by sven:

umm Larry not o nitpick, but 11h is TOW Gunner and 11C is mortar man.

sven(ex11h)

[joke]Thanks for reminding me how much of the details I've forgotten since I got out and how stupid I feel. [/joke]
Really, thanks for the correction, you are correct of course.

sven · Post by **sven** » Tue Jul 10, 2001 8:09 pm

Originally posted by Larry Holt:

[joke]Thanks for reminding me how much of the details I've forgotten since I got out and how stupid I feel. [/joke]
Really, thanks for the correction, you are correct of course.

I meant no offense. Hey they killed the 11H mos a few years back. Now it is a sub designation of 11b or 11m.

sven

Larry Holt · Post by **Larry Holt** » Tue Jul 10, 2001 9:19 pm

Sven, no offense taken, that was the intent of the [joke] tags.

As to the ability of mortars to fire directly at targets, vice indirectly. I have no information on WWII Polish mortars but I did check out the US Militart history site. http://carlisle-www.army.mil/cgi-bin/usamhi/DL/showdoc.pl?docnum=711 page 9 of this PDF lists the US 81mm mortar. It lists the M4 sight as well as the M7, M8 & M9 aiming posts. It lists no direct fire sight. I do not believe that WWII mortars had direct fire sights. I believe that they had to walk rounds onto the target.

BA Evans · Post by **BA Evans** » Tue Jul 10, 2001 10:26 pm

Artillery effects are abstracted. When you get a 'hit' with artillery...all that means is that the round landed close enough to affect the vehicle. It does not necessarily mean the round struck the vehicle. Your 'hit' very well could be an airburst over the target, concussion from a near miss, or an actual direct hit.

BA Evans

Originally posted by Larry Holt:

I agree and if I was getting killed by airbursts I would have no complaint. I was consistently getting killed by rounds coming down through the tree canopy and striking directly on the front (not the open top) of the vehicle.

[ July 10, 2001: Message edited by: Larry Holt ]

Larry Holt · Post by **Larry Holt** » Tue Jul 10, 2001 11:44 pm

Originally posted by BA Evans:
Artillery effects are abstracted. When you get a 'hit' with artillery...all that means is that the round landed close enough to affect the vehicle. It does not necessarily mean the round struck the vehicle. Your 'hit' very well could be an airburst over the target, concussion from a near miss, or an actual direct hit.

BA Evans

I agree that there is a lot of abstraction in the game. However vehicles are abstracted as the eight slab model. The "hit" has to have some armor value to compare the HE penetration against. I keep getting frontal (because my track was facing the mortar) hits that catestrophically kill, not turret hits that you would expect from above. Then again the arty model can simulate a direct hit as well as secondary damage (tool box, suspension damage, etc.) I do not think that a few pounds of HE detonating nearby my frontal 15mm of armor can penetrate it. There isn't even a baseplate to hurl (as a large piece of frag) through the armor.

[ July 10, 2001: Message edited by: Larry Holt ]

Grumble · Post by **Grumble** » Wed Jul 11, 2001 1:09 am

Larry,
My, admittedly ancedotal, experiences with mortars as anti-armor weapons parallels yours-especially with mortars of 40-50mm, basically grenade-throwers. Yeah, I know that each "shot" represents a few lobbed rounds, and mortar bombs have a high explosive-weight ratio, but the kill percentages noted here approach those of dedicated anti-armor weapons. Which means the round had to IMPACT the vehicle AND the blast had to be powerful enough to outright rupture the armor plate, concuss or cause enough spall/loosen rivets to kill the crew. I dunno...

Slayer · Post by **Slayer** » Wed Jul 11, 2001 1:55 am

Just out of curiosity, were the 81mm mortars unes in the test x1, x2, or x3. If it was x2 or x3, it could explain the accuracy, as it is really 3 mortars being lobbed, for 3X the chance of a hit. Just a thought...

New York Jets · Post by **New York Jets** » Wed Jul 11, 2001 2:27 am

Originally posted by Larry Holt:
Sven, no offense taken, that was the intent of the [joke] tags.

As to the ability of mortars to fire directly at targets, vice indirectly. I have no information on WWII Polish mortars but I did check out the US Militart history site. http://carlisle-www.army.mil/cgi-bin/usamhi/DL/showdoc.pl?docnum=711 page 9 of this PDF lists the US 81mm mortar. It lists the M4 sight as well as the M7, M8 & M9 aiming posts. It lists no direct fire sight. I do not believe that WWII mortars had direct fire sights. I believe that they had to walk rounds onto the target.

The 81mm Mortars seen on the TO&E's of many nations at the start of WWII were in most cases a licensed built copy of the French Mortier de 81 mle 27/31 designed by the Edgar Brandt firm in 1927. The US used a license built Brandt, as did the Italians (close copy), the Russians (actually a slightly redesigned 82mm close copy), the Japanese (actually the Stokes-Brandt, nearly identical to US version), the Nationalist Chinese (I will assume Communist also), as well as the Polish and a number of other minor nations.

Note: The US M2 60mm was also a license built copy of an original French, Brandt design.

As for direct fire sights. They did not exist in the sense of a "line up the front sight with the peep hole and let 'er rip" method. They did exist in the form of a mechanism that allows one to simply calculate range to target and adjust the angle of the tube accordingly. Some also required the personnel to adjust the level of propellent either with an adjustable port at the base of the tube or in the round itself. An experienced crew would have no trouble making things "warm" for you in short order if not with the first round.

[ July 10, 2001: Message edited by: Chris Trog ]

Nikademus · Post by **Nikademus** » Wed Jul 11, 2001 4:11 am

Originally posted by Larry Holt:
Thanks for the R/4 correction and the detail!

Can anyone address the penetration of 37 & 39 when the OOB gives a 28 HE penetration value?

In a conversation i had with Paul on Rifle Grenades, he told me that the variance for HE and HEAT based weapons (include grenades in this and morters as HE was also discussed)
the actual penetration can range from 50% - 150% of the stated pen at 'X' range.

Paul Vebber · Post by **Paul Vebber** » Wed Jul 11, 2001 4:22 am

ATucally teh variation has been redone a few times since then - the last iteration FOr HEAT is something like

wpnPen*(125-Die(20)-Die(20)-Die(20)))/100

So if you are REALLY lucky you can get up to 122% of the listed value and if REALLY unlucky as low as 65% of teh value but for teh most part it will be between 80 and 110% of the listed value. There is a 15% chance of a "tumpble" that prevents the jet from forming and that reduces the penetration to about 1/3 normal.

HE now has a kinetic factor so range slightly affects it, espeically if it ricochets and the blast goest mostly away from the armor.

Larry Holt · Post by **Larry Holt** » Wed Jul 11, 2001 9:11 pm

Paul,

Since you are informing us of formulas can you update us on the aror penetration is used to be something like
armor*(sqrt (1/cos(h_angle*pi()/180^2.8)+... and how about the normalization to 0 angle and slope?

There is so much under the hood that tantalizes us.

Larry Holt · Post by **Larry Holt** » Wed Jul 11, 2001 9:13 pm

Originally posted by Chris Trog:

The 81mm Mortars seen on the TO&E's of many nations at the start of WWII were in most cases a [snip as a libation to the bandwidth gods]

[ July 10, 2001: Message edited by: Chris Trog ]

Excellent post!! Can you give me some sources as I need to learn more about WWII mortars hardware and tactics.

Paul Vebber · Post by **Paul Vebber** » Wed Jul 11, 2001 10:10 pm

I've adjusted some of the formulas and they are not easily typed in given the limits of the forum.

THere are two ways to figure "compound angle" he vertical angle is the same in both, in the "LOS" method you take 1/(cos(V)*cos(h)) That gives teh LOS distance through the armor. Now if you rotate teh plate not about the vertical axis, but the axis through the plate, you get the funky SQRT(1/cos^2(v)+1/cos^2(h)-1) formula.

For teh methodolgy I use (changing those ^2 to other powers as a function of T/D (thickness to diameter ratio) I get better agreement with published "slope modifiers" than with the "true LOS" value.

The path a shell actually takes through the armor is not a straight line path, but a curved, sometimes S shaped path so the "full LOS" thickness using the proceedure I came up with tends to overestimate "effective thickness" so I stayed with the "funky" one.

For Combat Leader A totally new proceedure will be used, derived from the data in Lorrin Bird and Robert livingston's book on WW2 Ballistics. Sincle CL will deal with Modern too there will be some differences from the methodolgy there in some cases.

IF you want to understand the complexities of the whole penetration process, there is no better reference!!