What thickness of human flesh would have the same protective value as 100mm of RHA?

Question

I'm trying to judge how much damage modern anti-tank weapons would deal to giants and I'm looking for a rough, order of magnitude estimate on how much protection layers of flesh would provide.

Answer 1

Mythbusters did something tangentially like this:

[How much muscle is bullet proof][1]

Here's your problem - against muscle, 14 inches of Cow Muscle was insufficient to stop small arms fire - IIRC they started with a 9mm handgun round - which penetrated.

In the test(s) for the episode, if a 9mm penetrated, the went to a .45 round, then to a .223 rifle round etc. Muscle didn't stop the 9mm round.

Now, let's remind ourselves - muzzle energy of a 9mm is ~600 joules...

A 120mm smoothbore APFSDS round from an M1 Abrams has 12.1 MJ of Muzzle Energy.

In short - no amount of naturally occurring organic matter that could exist on a living, moving creature is stopping a Tank Round.

edit

I know this doesn't directly answer the question, and is more of a frame challenge - but seeing as your comments said it was for napkin maths, I trust it shows that without magic/unnatural materials, a Giant is going to pop like a cherry. [1]: https://mythresults.com/coffin-punch

Answer 2

It's Impossible

Modern armies will use thermobaric weapons.

A thermobaric warhead is similar to a fuel-air explosive in that it spreads a flammable mixture in the air and then lights it up; except it's spiked with thermite compounds for a hotter fireball. They also look awesome when going off.

Take the iconic RPO-A Shmel, for example, a.k.a the Shaitan-Tube. It is notorius for sucking in and burning the oxygen completely in the affected area, along with a blast force of about 5.5 kg of TNT, rivaling 155mm shells in destructive prowess.

Soldiers are near the explosion (within a 50 m^3 sphere) are immolated immediately, leaving only ashes behind. Soldiers further out will receive severe barotrauma and suffocate to death, as they find the air in their lungs sucked out, then forcibly replaced with a mixture of almost pure nitrogen.

Even if your giants are skyscraper-sized, that means any landing shots will:

• gouge out a huge chunk of flesh and turn it to ash;
• leave an even huger chunk of flesh seared and roasted;
• send shockwaves across the body, rupturing internal organs and causing severe internal bleeding;
• suffocate the giant by creating a zero-oxygen environment around it and inside its giant lungs.

If it's not dead after that, it's guaranteedly unconscious and open for a finishing blow. In a 3600F fireball, living tissue will happily burn by itself.

And yes, thermobaric weapons do come in bigger, meaner packages than a measly bazooka. In a fight between a single (let alone a platoon of) TOS-2 "Tosochka" and the Godzilla herself, I'm betting my money on the Tosochka.

Answer 3

About 300mm

This video shows various numbers of leather sheets stopping bullets of various calibers. He does not say how thick they are exactly; so, I will estimate that they appear to be about 3mm each. Leather is skin and from what I know, leather is not significantly tougher or weaker than the skin it is made from. The illusion most people have of leather being much tougher comes from trying to compare cow leather to human skin which is several time thinner, but actual penetration tests of leather with the skin of the animal it comes from typically comes out about the same.

These figures are pretty consistently about 3 times greater than the stopping power of these same weapons against RHA. So, if your giant's skin is about as tough as cow leather, then you need about 300mm of skin to equal 100mm of RHA.

• .22 long = 9mm of penetration
• 9mm FMJ = 39mm of penetration
• .45 APC FJM = 24mm of penetration
• 10mm FJM = 45mm of penetration
• .44 magnum = 66mm of penetration
• .50 cal Desert Eagle = 72mm of penetration

That said, keep in mind that 300mm of skin is not going to come close to stopping modern anti-tank weapons. In fact, most anti tank weapons could probably pernitrate closer to 3000mm of skin using these figures; so, if you shoot any sort of anti-tank weapon at a giant with 300mm skin, assume it will be a kill shot.

This assumes you mean a standardized RHA testing steel

When talking about how different weapons pernitrate RHA steel, you are typically talking about mil-dtl-12560k or some other country's equivalent there of which is a hardened high-carbon steel with less than 1% manganese and no other elements added. This is NOT the best grade of armor steel out there, and is in fact not used in most military applications anymore. There have been better grades of armor steel since the late 1800s, but the reason that mil-dtl-12560k steel is used in ballistics testing is because it is standardized.

So, when one manufacturer tries to sell a bullet and says it can pernitrate 4.5mm of steel and another manufacturer says theirs can pernitrate 6mm of steel, the defacto assumption is that they are talking about this particular type of steel.

A lot of modern armor has all sorts of additives that can make it several times tougher than the RHA standard. A bullet rated to pernitrate 20mm of RHA might be stopped by a 9mm plate of body armor. So, while 300mm of skin is about 100mm RHA equivalent, there are also types of steel armor out there that are only 25-30mm thick that are 100mm RHA equivalent.