Abrams Side Armor

[lavictoireestlavie]

According to Tom Clancy's Book ,Armored Cav: A Guided Tour of an Armored Cavalry Regiment.:

"...M829A1 "Silver Bullet" APFSDS rounds from other M1A1 Abrams were unable to penetrate the front and side armor (even at close ranges) in friendly fire incidents as well as an incident in which an Abrams tried to destroy an abandoned Abrams stuck in the mud."

I got the impression that a 1988 Model Abrams M1A1 HA will not shrug off M829A1 rounds into its side hull or turret. I assume they just exaggerated and the projectile actually hit the turret at a specific angle within the frontal 60 degree protection arc.

What are your thoughts ?

[Volcano]

Probably not 90 degree shots on turret side. I cannot imagine any turret side withstanding an M829A1 at 90 degrees. :shocked:

[Maj.Hans]

I thought that the armor on the turret sides was still relatively thick, even if it was nowhere near as strong as the front. Like Volcano said I wouldn't expect it to stop a square hit from an 829A1, nor would I expect nearly any tank to do it, but perhaps if the side armor was struck obliquely?

[Ssnake]

Clancy was ... very enthusiastic.

[hoggydog]

example -

In his 1986 novel Red Storm Rising, Tom Clancy featured the "F-19A Ghostrider" (nicknamed "Frisbee" by the pilots and crew) as a secret weapon used to combat a Soviet invasion of Germany. This vehicle was considerably more capable than the F-117, being a supersonic fighter rather than a subsonic precision bomber. The F-19A as described in the book featured underwing hardpoints for various ordnance, including air-to-air missiles and BLU-107 Durandal runway-cratering bombs. The aircraft also has circular wings instead of angular ones, hence the nickname.

[outontheop]

The difference is that "Red Storm Rising" was a fictional novel, while "Armored Cav" is a non-fiction (or supposed to be) reference book.

Possible he meant "maintained combat effectiveness". After all, none of the M1s penetrated by RPGs in OIF were rendered combat ineffective (at least, the sources I've seen indicate as much). They had crew casualties and minor systems damage, but in a "real" war (read: Red Horde Crossing the Fulda Gap), they'd have kept fighting. The tank in the mud may have been penetrated, but of course the crew had already evacuated- they were looking to catastrophically burn out the tank, not merely penetrate it. The couldn't get it to brew up (and may not have been able to penetrate at all?)

Alternately, shot may have hit inert portions of the turret (actual crew space is much smaller than total turret size), or been at very oblique angles. Hard to say. I can imagine the side turret being resistant to 120mm apfsds, but it's certainly not "proof".

[daskal]

In terms of frontal armor penetration - the abandoned M1A1 "Cojone Eh" during the 1st Thunder run has also been shot by a Sabot round. I alwas thought the big hole on the frontal armour was due to this round:

[outontheop]

Isn't that the one that was abandoned and then hit by sabot AND maverick to prevent capture? I thought both the low front-right turret hit AND the right side hit were mavericks. Not many tanks will be surviving a 700 pound ATGM.

*edit* ok, I find some sources that say US sabot and 2x Maverick, some that say 1x Maverick and 2x Hellfire. A few claim a JDAM as well. All seem to agree the front turret hit is the Maverick. Hard to stop a HEAT warhead of that size- and it doesn't actually appear to have fully perforated the front array at any rate.

[Invader ZIM]

I thought that was a hit from an AGM-65 Maverick going by this report, actually two mavericks were required.

http://www.fprado.com/armorsite/US-Field-Manuals/abrams-oif.pdf

Took one thermite grenade, one sabot in turret ammunition compartment, and two Maverick missiles to finally destroy the tank. Ended up compromising the SAP armor package during the destruction process

Same photo is shown, with the two Mavericks pointed out.

[DarkLabor]

Sure, it's not a sabot.

You don't have the marks left by the fins (plus the size is not consistent with the size of the penetrator).

[outontheop]

I thought that was a hit from an AGM-65 Maverick going by this report, actually two mavericks were required.

http://www.fprado.com/armorsite/US-Field-Manuals/abrams-oif.pdf

Same photo is shown, with the two Mavericks pointed out.

Yeah...any tank that requires a 126 pound, 300mm HEAT warhead to get reliable frontal turret perforation is alright by me!

[Invader ZIM]

It seems in the report that they wanted more protection on the sides/rear, which would explain the large order for the M-19 ARAT-1 and ARAT-2 add on armor which is seen more often in the 2006 time period.

Seems to be pretty light as well:

outontheop, yea, I forgot the diameter of the HEAT warhead is massive, 300mm vs. the TOW's 152mm. Tough tank!

[dejawolf]

it's pretty much impossible for the side hull of the abrams to be impenetrable to M829A1, especially on the rear half.

this image shows the thickness of the hull side of the abrams tank.

and this image shows the thickness of the rear skirts, which is pretty much just sheet metal.

the front skirts are thicker, but still insufficient against rounds designed to penetrate up to 70cm of solid steel.

[Invader ZIM]

Even though the rear skirts are thin, I always thought the purpose of the skirt was to set off a HEAT charge at the improper distance to minimize it's full penetration potential on it's way to the actual hull.

[Grenny]

Even though the rear skirts are thin, I always thought the purpose of the skirt was to set off a HEAT charge at the improper distance to minimize it's full penetration potential on it's way to the actual hull.

To produce a standoff big enough to decrease HEAT effectiveness...the skirts would need to be 3 meters away from the Hull :-P

[Damian90]

M1's side hull protection is relatively advanced when compared to other tanks.

In the frontal part over driver compartment it is spaced array made from ~70mm thick ballistic skirts + ~60-70mm thick hull sides + fuel tank compartment + internal bulkhead.

Over crew/turret compartment it is ~70mm ballistics skirt + ~60-70mm thick hull side.

Over engine compartment it is several mm thick non ballistic skirt + ~30-40mm thick hull side.

Besides this, hull sides protection are optimized to provide adequate protection withint angles of safe manouvering, which is 60 degree's frontal arc of vehicle.

Turret sides are ~350-400mm thick special armor array (it is a NERA - Non Energetic Reactive Armor type). Also optimized to provide high levels of protection within vehicle frontal 60 degrees arc, but also relatively good protection for hit angles closer to 90 degrees.

Front lower hull is ~650-700mm thick special armor array.

Front glacis is ~50-60mm thick steel plate at 82 degrees inclination.

Front turret is ~850-900mm thick special armor array.

[Invader ZIM]

To produce a standoff big enough to decrease HEAT effectiveness...the skirts would need to be 3 meters away from the Hull

Ahh, I thought the standoff didn't have to be so large, I figured the optimum was the extention on the HEAT rounds endcap as referenced below.

Going by the Wiki: http://en.wikipedia.org/wiki/Shaped_charge

The location of the charge relative to its target is critical for optimum penetration for two reasons. If the charge is detonated too close there is not enough time for the jet to fully develop. But the jet disintegrates and disperses after a relatively short distance, usually well under 2 meters. At such standoffs, it breaks into particles which tend to tumble and drift off the axis of penetration, so that the successive particles tend to widen rather than deepen the hole. At very long standoffs, velocity is lost to air drag, further degrading penetration.

http://en.wikipedia.org/wiki/High-explosive_anti-tank_warhead

1. If the HEAT warhead is detonated too close to the target's surface there is not enough time for the particle stream to fully develop. That is why most modern HEAT warheads have what is called a "standoff", in the form of an extended nose cap or probe in front of the warhead.[notes 1]

The distance is critical because the stream disintegrates and disperses after a relatively short distance, usually well under 2 metres. The stream material is formed by a cone of metal foil lining, usually copper, though ductile iron and tin foil was commonly used during the Second World War.

So going by a 125mm Russian Heat round like this:

That standoff tip is only a hair over 8 inches. starting the jet when it hits the metal skirt of any tank, and then has to pass though air, then the roadwheels, etc. on it's way to the actual hull, would definately degrade it's effectiveness vs. if it struck the hull directly, right??

Or am I still missing something on how these things work?

[Grenny]

The Standoff-fuse is limited by space requirements and aerodynamics. It is usually NOT designed to offer the optimal standoff....but to give the optimal standoff within limitations.

On example is the SLAT armour used against the RPG rounds. If the round explodes, SLAT will actually INCREASE the effectiveness of the round, thankfully there are other mechanism that make SLAT work.

[Invader ZIM]

Ohhhh.

You have a point, that helps explain it then, I was definitely missing something.

I kept thinking of the copper cone like a magnifying lens, as soon you go outside of the focal distance, then the effectiveness drastically is reduced. (Think of focusing light with a magnifying lens on an ant, it would fry him, but pull the lens back a few inches, and he'll just get a tan instead.)

Thanks for the correction Grenny.

[DarkLabor]

It's is true that light has corpuscular properties but in the case of shaped charges, it's pure solide matter.

The dart formed by a shaped charge is the result of the copper propelled to a focal axis.

You start with a 100ish mm diameter cone and end up with a pencil size diameter dart.

The standoff distance is the required distance to turn the cone into a dart.

Under this distance, the cone consumes itself in the armor without having enough energy.

Take a look at this :

http://pds10.egloos.com/pds/200905/16/23/d0056023_4a0e22b0d92f2.jpg

The first charge is a flat charge, the copper is propelled perpendicular to the armor and shows how ineffective it is not to focus the detonation/copper/energy.

The second and third are most likely a representation of the influence of the cone. One being flat at the tip.

The last shows the effectiveness of the standoff and shows the path followed by the copper.

In general the standoff distance is nearly two to three time the height of the cone. Beyound this distance the dart doesn't improve it's efficiency nor it's small diameter.

One thing to keep in mind is that the dart goes faster in it's tail than at it's tip.

http://ars.els-cdn.com/content/image/1-s2.0-S0921509398006406-gr1.jpg

The tip is submitted to the air resistance as opposed to the tail.

When the tail no longer pushes the tip, the dart begins to loose it continuity therefor it's efficiency.

[Invader ZIM]

Wow!!

Thanks DarkLabor for the detailed explanation. I couldn't get the first link to open, but your description was good enough.

I certainly learned something new today, thanks again guys.

[DarkLabor]

And with this link?

http://img.xooimage.com/files87/f/3/d/132165484-3a2c7d3.jpg

[Rotareneg]

Slat armor is meant to either deform the shaped charge before it detonates to reduce it's effectiveness and/or damage the fuse so it doesn't detonate as designed.

Apparently the main reason why spaced armor in WWII worked against HEAT rounds was just because the old rounds weren't that great, which lead to the penetrating jet breaking up over a much shorter distance than modern shaped charges.

[Invader ZIM]

That pic works for me DarkLabor, thanks!

[GSprocket]

The description of the jet from Darklabour is wrong.

The tip of the jet is around 8km/s (reference to APFSDS at 1.7km/s), with a velocity gradient towards the rear of the jet, where it is "around" 1km/s.

Behind the jet is a 'slug' of material of much higher mass, but slower velocity.

Because of the velocity gradient, the HEAT jet is under tension, rather than compression, and the penetration performance is degraded if the coherence is lost - the initial stages of particulation often have minor effects, but as the jet breaks up there is an increasing chance that subsequent particles will erode the rim of the existing crater, rather than deepening it, and the mid and rear portions of the jet have relatively poor independent penetration capabilities.

This is why protection methods that aim at 'dwelling' or dispersing the jet have such high effectiveness against HEAT weapons compared to KE rounds, where the penetrator is much more massive and has similar penetration capability for fragments from any portion of it - the whole rod travels at the same speed, and the rear of the rod 'aids' the progress of the portions ahead of it.