A small history of the armour race

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Rolls Royce armoured car, designed 1914
(c) Hohum

The first armoured pars were created prior to the First World War and their armour was considered effective against rifle bullets. Machine guns weren't a major concern yet and the armoured cars themselves weren't a major concern either, so no dedicated armour-piercing (steel core) cartridges were introduced to meet the threat.

The next step were actual tracked (tracklaying) armoured vehicles, "tanks" (1916). Their armour was considered effective against the powerful rifles used by snipers to penetrate observers' and other snipers' protective steel plates in static warfare. The bulletproofing was effective enough that even steel core bullets of standard calibres were unsatisfactory. Even a special 13.2 mm calibre proved to be only moderately convincing.

These tanks were at no point shell-proof, though. Mountain guns (mostly cannons at the time) proved to be mobile and deadly enough against tanks, for example. The armour plates were so thin that normal high explosive shells with delay action fuse sufficed for a kill.

Char B-1bis, (c) Igor Kurtukov

The 1920's saw effectively no advance in applied tank technology, though the advance in component technology (gearboxes) was substantial. A top speed of 30 kph became normal only around 1930, and actual shell-proofing of tanks only in the late 1930's with the B-1bis and soon thereafter the Matilda II (but many other new tank types and versions were even in the late 1930's only bulletproofed). This development devalued the by then ubiquitous light anti-tank guns of 25-47 mm calibre.

The armour race during the Second World War is widely known, so I'd just like to point out that early in WW2 the Soviets didn't believe the Germans' claim that their best tanks were the Pzkpfw III and IV models, since the armour schemes of their own T-50/T-34 and KW-1 developments were much more ambitious and they expected a proper counterpart. The Germans in turn were largely ignorant about this new development and as unpleasantly surprised on the battlefield as already in 1940 by the Matilda II and B-1bis.

T-44 armour scheme
The glacis was almost impenetrable due to thickness and slope.

The end point in WW2 was very heavy armour on very heavy tanks and very smart armour schemes on some tank designs of medium (T-44) or light weight (Jagdpanzer Hetzer / G-13). The introduction of shaped charges during the Second World War introduced an entirely new principle of armour penetration, and a brute force approach of high explosive squash head / high explosive plastic was invented as well. The by then three principles of armour penetration made the development of an armour scheme much more difficult.

Yet again, wartime tanks lingered on and little happened in the immediate post-war time.

The Korean War did little but teach Americans respect for the T-34/85. The long overdue replacement of the original Bazooka and some early 57 mm recoilless guns by larger calibre weapons was triggered.

The first post-war designs of the West mostly used British 17 or 20 pdr cannons or American 76 or 90 mm cannons. All of these proved to be unsatisfactory once a T-54 tank (an upgunned T-44) was driven onto a Western embassy during the 1956 Hungarian uprising and measured. Only then did the West understand (again) that the Soviets weren't striving for satisfactory armour protection only on their heavy tanks such as T-10. Their medium tanks were well-protected as well. The response was the 105 mm L7 gun, the first de facto standard tank gun of NATO.

The T-62 arrived soon thereafter, and was well-respected after the T-54 shock. The Israelis soon learned that its armour protection was actually not substantially better than the T-54/-55 series'. The resistance to HESH had been improved by the Russians during the late 50's, though.

T-64

The Russians had kept a calibre superiority for most of the time since 1940, going from 76.2 mm to 85 mm to 100 mm to 115 mm calibre* in their medium tanks. The T-64 and T-72 series finally employed the 125 mm calibre which is still in use today and still larger than the Western one's.

Yet again their adversaries misunderstood their armour: The T-64 and T-72 tanks retained the cast, rounded turret armour which doesn't suit itself well to non-steel inserts, and the West thus expected homogeneous armour. There were inserts, though. As a result, the West was fooled into believing that 105 mm was still satisfactory and kept this calibre longer, the Americans well into the 90's (M1A1 Abrams with 120 mm appeared in the 80's, but USMC kept the M60 into the 90's).

It was the Germans who distrusted this and created the new smoothbore 120 mm calibre during their Leopard 2 main battle tank development, which became de facto NATO standard.

The Leopard 2 was also the first MBT of a new Western generation, which challenged the Soviet 125 mm calibre to its limits with a turret front and glacis protection strong enough (due to the new so-called Chobham armour scheme). This kept 125 mm munitions in check throughout the 80's, but by the end of the Cold War refined Soviet penetrators had caught up, and some Western Chobham armour generation tanks were upgraded with stronger turret front armour.

The Chobham armour generation tanks had a risky bet running; their designers did bet that the enemy was in front of the hull or turret. This was risky, as the relatively mobile tank tactics of this tank generation made use of much movement, so the hull sides were exposed to a single point of threat not only during surprise contacts, but also during regular movements on the battlefield (Wedelfahrt, S-line movements). The Soviet designs had a bit less of a problem with this since the autoloader and reduced maximum crew member sizes allowed for a lower hull and their smaller turrets were protected against a wider arc.

T-72 covered in ERA tiles

Yet again the Soviets had fooled the rest of the world in another aspect; their introduction of explosive reactive armour tiles (another early adopter was Israel) devalued most in-service shaped charge munitions. Western companies kept developing and offering new but already obsolete single stage HEAT warhead munitions well into the 1980's. Germany introduced its answer to T-64/T-72 - the Panzerfaust 3 - only after the Cold War, then obsolete against the latest Soviet/Russian armour since a decade already.**

Western armour faced Soviet-made Iraqi armour at the end of the Cold War, and killed it easily for many reasons - including the fact that its protection levels ranged from Soviet 50's to Soviet 70's armour grades, and met Western anti-tank weapons meant to penetrate Soviet 70's armour. This misled the public more about the relative strengths of Western and Soviet/Russian armour than it did mislead the experts, of course.

And again, even though the Cold War was no World War, tank development lapsed afterwards, with no all-new main battle tank developed since in Europe or North America.Upgrade packages and new munitions were introduced, though. The Russians finally met a design ceiling of their 125 mm calibre; the new long rod penetrators were restricted in length growth by the two-piece ammunition of the 125 mm calibre.

up-armoured Challenger 2, post-2003

The conflicts of the post-2002 period have broken up the late Cold war's paradigm of 'front armour first'; the protection of the sides and rear against shaped charges, the belly against mines and the roof against bomblets has been increased on many tanks with upgrades. The side protection against shaped charge threats doesn't appear to be overpowering, though; 105 mm and especially the even larger calibres of HEAT appear to still be capable of penetrations.****

Neither hyper velocity missiles nor larger calibres (Western 140 mm, Russian 135 or 152 mm) were introduced into service. A longer 120 mm (L/55) gun, replacement of old 105 mm-armed MBTs by mostly second hand 120 mm-armed MBTs and new 120 mm APFSDS munitions were the increases of armour penetration capability instead.

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Are there any lessons? Well, I think so. 

The armour protection of the Soviets (a closed society) were typically underestimated for a meaningful period after every substantial improvement. NATO had unsatisfactory penetrative power against top-of-the-line Soviet tanks during much if not most of the Cold War.

Penetration advances were furthermore always reactive to armour increases; there was never a new weapon introduced for the sole purpose of getting a much better penetration capability while the present in-service penetration capability was considered satisfactory. This happened with munitions at times, but not with guns.

Armour protection was never truly satisfactory without sacrificing mobility. There have always been weak spots and at least some common threat munitions were at all times capable of penetrating weak spots (even frontal ones, such as the gunner's sight).
It's also noteworthy that even tanks with impervious plating would still have mission-critical vulnerable exterior equipment. A hit on sights, running gear or the cannon barrel would still result in a mission kill. This does to some extent discourage a tank design priority on protection over firepower and mobility unless a zero casualty mindset dominates during a war of occupation.

S O

defence_and_freedom@gmx.de

*: Facing mostly 50 mm/short 75 mm, 75 mm, 76 mm/17pdr, 105 mm respectively.

**: This is an as embarrassing story as the Keiler's.

***: (excluding the Merkava and to some degree the Challenger) 

****:  A shaped charge's penetration is roughly proportional to its diameter at a given state of technology. It began with 1:1 and was improved to beyond 7:1. Another important variable is the liner material, with tantalum being much better and much more expensive than copper. Tantalum is considered reasonable only for PGMs.

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