Jump to content
Sturgeon's House

How Exactly Does Sloped Armor Work, Anyway?


Recommended Posts

Ok, let's go with say, a 30 degree slope, which a vast assortment of shells in WW2 were tested against, basically, when a plate is facing completely perpendicular, It's exactly as "thick" as it will be on paper performance wise,  however, when you lay out out at 30 degrees, suddenly the projectile has to penetrate it at a diagonal, so, even though the plate didn't get thicker, it effectively still has to penetrate more of the plate then it would if it were facing perfectly upright because it now has to get through said diagonal angle as opposed to a perfectly straight path.


However, when a slope gets to around 60 degrees or more, this is where many projectiles really struggle, because, at least in the days prior to modern long rods and improved fuzes, projectiles require a good "bite" angle or there's a large risk of the projectile, particularly a higher velocity one simply deflecting due to the fact it can't keep that bite on the target and smash it's way through, or, even worse, a strike at a steep angle will also subject a projectile body to severe uneven distribution of impact stress which can cause it to shatter outright, a projectile that shatters will basically lose almost any chance it has of penetrating due to the loss of the strength of the projectile and the energy now being disspated everywhere in several smaller fragments instead of focused in one large one.


Ironically, as I've pointed out before on how this affects smaller, higher velocity rounds worse due to them being more likely to deflect or shatter at such high speeds, this is why, even though APDS and APCR from guns such as the 20 pounder and various 90mms the US used late and post war have similar or higher penetration "on paper" then the slower 120mm AP round of the M58 gun, the former would bounce off something like the front of a T-54/55 or IS-3 even at point blank range, whereas the M103 could penetrate them at a pretty good distance.


As for HEAT, It's not that the shells themselves couldn't penetrate, infact, 90mm M348 HEAT could penetrate even the front of an IS-3 or potentially an IS-4, the problem is, mainly with earlier HEAT designs, they had terrible fuzing, and with the M348, which is noted here because it's one of the most notorious cases due to it's particularly flawed design, it was based solely on the nose striking at a good enough angle to reliably detonate the fuze while facing the armor plate (the fact the M348 was designed without a well designed standoff didn't exactly help this), however, if the slope is so steep the round glances off before the fuze can be triggered, well.... It's basically useless.

Link to comment
Share on other sites

This is the chart from Technology of Tanks showing the "effective" thickness vs. the LOS thickness of sloped RHA vs. APDS type projectiles:




The solid line tracks the ratio of LOS thickness to normal thickness, while the dotted line tracks equivalent protection vs. normal thickness.


This is why you had weird shit in tests like the 20 pounder being able to penetrate the T-54's turret, but not its hull.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


  • Similar Content

    • By T___A
      This shall be the general thread for all things soviet tanks. I shall start by posting an article I just wrote for my blog. I would recommend Archive Awarness which is an excellent blog about Soviet tanks and their experiences with other nation's tanks.
    • By Collimatrix
      At the behest of @Lord_James, this shall be the thread for general discussion of conventional passive metallic armor.  Whether it's steel, titanium, magnesium, exotic laminates of all three, this is the thread for it.
      In answer to your earlier question, Lord_James, relatively small amounts of boron, in steels that have the appropriate levels of carbon, form intergranular barriers that dramatically slow the diffusion of carbon out of the austenite crystals during quenching.  Long story short, this means that the depth of material that can be effectively hardened is much greater.
    • By Must Be Spoon Fed
      I'm interested in Soviet armor production and deployment. Especially of T-55 tank and its variants. Sadly, most sources touch this subject very generally while I would want to get a more detailed view. How much tanks were produced in which country and at what year. Were Soviets producing armor for themselves or for export. Any source which would go into bit more detail about it is appreciated. I would appreciate if someone could help me find information required about those tanks as so far I can rely only on quite general information. 
    • By SirFlamenco
      I want to calculate the weight required to make an armor that can resist 7.62 RUAG SWISS AP, also known as VPAM level 12. I needed a baseline so I took NIJ Level IV and then tried to find the difference of weight so I could get a percentage. The only plate that's still made for this threat is the TenCate CX-950 IC. This plate is 8.93 lbs for a sapi medium and is alumina in-conjonction with soft armor. I then needed to find a Level IV alumina IC, which I found on UARM's website. It's 7.6 lbs, so if we do 8.93/7.6 we get around 1.175, but I put 1.25 considering UARM's plates are often quite heavy. Now that we have 1.25, we can start applying it to silicon carbide and boron carbide. Denmark's group has a level IV silicon carbide plate at 5.95 lbs, so times 1.25 it gives 7.4375. Hesco's boron carbide IV plate is 5.1 lbs, so times 1.25 we get 6.375.
      Now, I wanted to know what was the weight for hardened steel. I took MARS 600, which is one of the best armor steel you can get. Using this page, I can easily calculate that you would need about 19mm to stop it. Using a calculator, we know that a full inch sapi medium plate would weight 33.9 lbs. 19mm/25.4mm = 0.748 inch so if we do 0.748*33.9 we get 25.3572 lbs. 
      The problem is obvious : How is boron carbide 4 times as light as steel? Silicon carbide is 3.4 times as light too? It doesn't make any sense, giving that they are both around 2.2 ME and hardened steel is 1.3 ME, so it should be around 1.7 times heavier for steel. What did I get wrong? 
  • Create New...