Notes on Modern Armor

by Nathan Okun
Updated 27 March 2002

Modern laminated tank armor (Chobham, etc.) is designed to resist penetration by ultra-high-velocity APFSDS projectiles and HEAT (shaped charge) needle-like focused metallic or glass jets.  It is especially designed to disperse such concentrated impacts and to absorb the huge thermal effects of such penetration attempts.  Against a huge, slow-moving hard-capped steel AP projectile, the advantage of using this kind of material is not as large, though the great thickness of this relatively lightweight armor compensates to a large extent.  This armor material is very unlike face-hardened solid steel, which is rather heavy and not as strong as the best non-metallic materials (kevlar, etc.), but also more difficult to cut using shearing action due to the large thickness of soft back in the face-hardened plate.  On an equal-weight basis, kevlar and similar lightweight armors would be much superior to any kind of solid-steel armor when the non-metallic armor's surface is protected from cutting action of flat-nose and similar projectiles - damage to the projectile will not be a primary method of increasing armor protection, as it is in face-hardened armor or in all armors against deformable or brittle projectile materials (lead bullets, for example).

The so-called brass "cop killer" bullets are fired at high velocity (they weigh much less than lead bullets of the same size), have a flat nose for maximum shearing effect, and do not deform much on impact, which is why most regular bullet-proof vests do not do a very good job of protecting against them; if the kevlar in the vest could be kept from being cut by the edge of the nose of these projectiles, it would be much more effective, though not as effective as against lead bullets that flatten out on impact.  Face-hardened armor tried to do the same thing to steel AP projectiles, which is why a good projectile AP cap would allow its defeat more easily, as it reduced or prevented projectile damage from the impact.  However, when extremely high velocities are used, thermal and shock effects become the most important factors and neither kind of armor (cloth-type kevlar or hardened steel) is best, as it burns and/or melts or, at the very least, flows out of the way of the projectile due to being heated to a soft, plastic state.

The projectile nose/jet tip is also undergoing a similar reduction, but that is why they are so long, to allow a considerable reduction and still eventually punch a hole in the armor (even a small hole punched by a rather small remaining portion of the projectile/jet is very dangerous due to the heat and high velocity of the projectile/jet, which is not reduced much during the penetration until the projectile/jet is entirely consumed if it fails to penetrate).

Since naval projectiles did not go very fast, none of the advantages gained by the thermal effectiveness of these lightweight armors means much and the mass and strength of the armor is much more important in stopping such projectiles - as mentioned, though, many of these materials, if protected from cutting action, are extremely strong for their weight and would be better than steel.  Use of such lightweight armors is good for protecting ships from fragments and blast effects and some small missiles, but the weight required against large missiles, especially supersonic missiles, is prohibitive in anything but a very large warship (battleship or aircraft carrier).

Large ships are unfortunately expensive and take a long time to build.  They consume a lot of resources, money and manpower.  They also can only be in one place at one time, so they can be bypassed unless they are located at some kind of choke point.  Thus, it is better to build a larger number of the ships with the minimum adequate functionality than few very large ships (such as at the World War II Battle of the River Plate, for example, although the British cruisers were rather too unprotected and the smaller two had weapons that were inadequate) - however, just what is "good enough" is not easily analyzed and failure means a bad result in future battles!  For example, if Germany had built a large fleet of Pocket Battleships before World War II, instead of the fewer BISMARCK and SCHARNHORST class ships, they would have been better off during World War II (since they were always outnumbered by the British Fleet anyway, trying to build bigger ships just meant a bigger number of people lost when the ships were sunk).  Did being big help BISMARCK?  No.  But, say that there were three Pocket Battleships in the same scenario.  They could have split up and run away from the British, remaining a threat for months, not just a few days, even if one had been ganged up on and sunk, as with BISMARCK.


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