This week's highlight is "Ilyich's Eyebrows", also known as "BDD armour". Excerpt taken from the T-62 article.
All T-62Ms are equipped with applique BDD armour, and older T-62s may be retrofitted. BDD armour is more popularly known as "Ilyich's Eyebrows" in reference to Soviet Premier Leonid Ilyich Brezhnev:
BDD armour covers the hull glacis and the turret front on either side of the gun, but not the lower hull area nor the turret top. It is a form of NERA armour, composed of a laminate of alternating steel plates and a polyurethane filling. First entering inventories in 1980, BDD armour boosted the T-62's protection level close to that of the T-64 or T-72 Ural, giving it the ability to resist widespread 105mm APDS ammunition as well immunity from lightweight portable anti-tank rockets like the LAW and RPG-7 families.
The coverage offered by "Brow" armour was very good. Although the size of the NERA armour blocks is rather small, the turret cheeks are mostly covered. On the right side of the turret, the NERA covers an arc of just under 50 degrees over the turret cheek, while the remainder is covered by the front steel plate. On the left side, the NERA block covers an arc of just under 46 degrees, and the front steel plate covers the rest. Overall, "Brow" armour covers the frontal 140-degree arc of the turret, except for the mantlet area. The diagram below shows the mounting points for the armour kit.
Method Of Operation
The single hull block is 150mm thick - or 300mm thick taking into account the hull sloping - complete with an array of steel plates within. Each internal steel plate is just 5mm thick, and the polyurethane layer fills the gaps in between. The front wall is 30mm thick, or when angled at 60° as the glacis is, 60mm thick. The internal steel plates are angled at 65°.
The turret blocks are uniformly 296mm thick, but the front plate becomes thinner as it curves upwards. The front plate itself is cast steel, 71mm thick at the top half and 85mm at the bottom half. The added thickness compared to the glacis plate is intended to compensate for the relative weakness of cast steel, which is only about 90% as effective as generic rolled steel, and to compensate for the positive influences of the high slope on the glacis. The internal steel sheets in the turret array are the same thickness as in the upper glacis, 5mm, but they are angled at 50° instead of 65°. However, the relative thickness of the armour blocks on the turret are much higher due to the round shape of the turret and the blocks, so the smaller angle is less relevant for a head-on impact. When impacted at a side angle, the relative thickness of the blocks is less, but the angle of internal steel sheets is greater.
"Brow" armour most likely operates on the transfer of kinetic energy from impacting projectiles to the thermoplastic polyurethane (TPU) layer through the propagation of shockwaves from the impact of the attacking penetrator. The TPU would penetrated, so it has some erosive effect, but it should also be violently displaced out of the penetrator's path. However, the function of the thin steel sheets embedded into the TPU layer is not so clear.
One possible mechanism would involve the reflection of shockwaves from the surface of the thin metal sheets at an oblique angle to the penetrator, thereby pushing a greater mass of TPU into the penetrator. This would be mostly useless against APDS or long rod penetrators, but it should be quite effective against shaped charge jets, as TPU is a low density material suitable as a barrier against shaped charge jets.
The use of a high density front plate paired with a low density filler is principally identical to the original upper glacis armour of the T-64A. The high density front plate has the function of not only eroding an attacking shaped charge jet, but also particulating it. A low density filler would perform effectively against a particulated jet, and reducing the density gives better results. For the upper glacis armour of the T-64A, the low density filler is glass textolite, with a density of 1.3 g/cc. TPU has a density of between 1.1 to 1.2 g/cc, making it highly optimal for this application. Coupled with the reflection effect and the additional erosive effect of the steel sheets themselves, the armour kit should be quite effective against shaped charge warheads. However, low density fillers generally do not have much effect against KE penetrators, so some of the protection from the armour blocks (outside of the thick steel front plate) should be from the embedded steel sheets. Although the thickness of the sheets is insufficient to significantly erode any long rod penetrator, the sheets may still contribute by causing the tip of a penetrator to ricochet off, leading to a reduction in penetration potential from the loss of penetrator material and from the deformation of the tip. The subsequent impact of the penetrator on the base armour would be rather inefficient due to the deformed tip.
Another possibility is that the displacement of the TPU causes the steel sheets to bulge away and downwards laterally against a penetrator. This lateral motion would have the effect of either disturbing the delicate flow of cumulative jets or damaging a kinetic energy penetrator by creating stresses in the body, which are suddenly released, causing the penetrator to fracture. However, the presence of TPU behind each steel sheet would reduce the bulging velocity of the sheets, making them less effective, so the effect of the movement of the plates is probably quite minor compared to its value as a simple spaced barrier. A more detailed explanation is available in Tankograd's T-72 article. Even if it is unlikely that the bulging of the steel sheets has a big contribution to the overall protection, it does not mean that "Brow" armour cannot be labelled as a form of NERA. The reflection of shockwaves from the steel sheets embedded in the TPU is certain to occur, and this is already sufficient to qualify it as NERA.
The armour kit gives uncompromising coverage of the upper glacis, but the turret front is only partially protected by the NERA armour. The two "brows" weigh 1.8 tons together, and the upper glacis block weighs about 1.5 tons. Equipped with the additional armour, the T-62M bloated to 41.5 tons, 3 tons greater than the vanilla T-62, and about the same as a T-72 Ural.
A Hungarian test at the end of the Cold War showed that the side of the turret of a T-54 equipped with "Brow" armour (taken from a modernized T-55) could not resist a Fagot missile. The results of the test are detailed on this TankNet post. This effectively means that the "Brow" armour for the turret, plus 120mm of cast steel, cannot resist a shaped charge warhead with 400mm of penetration. However, the front of the turret of a T-62 has much more than the side of the turret of a T-54 (242mm vs 120mm), so there is no reason why it cannot resist a Fagot missile or something similar.
The video cannot affirm or disprove anything, as the missile struck the turret approximately where the gun breech is. There is no way to know if the missile defeated the side armour or not, because even though the loader is fine, this could be because he was seated below his hatch, meaning that he would not have been in the line of fire had the missile perforated the base armour. If the missile did not manage to get through, it is still more than possible that the crew bailed as a matter of principle.
The T-62M can be considered on par with or even superior to the T-72A, but much inferior to the T-72B in armour protection against both KE and CE threats. "Brow" armour leaves the mantlet area uncovered by the NERA armour array, but at least the thick steel wall of the BDD blocks forms spaced armour over the machine gun and gunsight ports. With the applique armour, the maximum total thickness of the turret armour of the T-62M is 512mm (296mm BDD block plus ~70mm air gap plus 200mm turret) over the areas covered by the NERA armour. The total amount of steel is less than in the T-72A turret, but needless to say, it should be self evident that the NERA array and airspace combo is more effective than "Kvartz".
Judging by the configuration of the BDD blocks, 105mm M735 APFSDS would not be sufficient against a T-62M from the front where the NERA array is present, not to mention M392 and L28 APDS. The area over the machine gun and gunsight ports is definitely resistant against M392 or L28 as the 71-85mm spaced plate should effectively de-cap the tungsten carbide core and fracture the core, whereby it is broken up inside the nonmetallic filler before it reaches the ~242mm turret front. Even without the spacing, the added thickness of steel is likely to be enough to defeat the shell.
Even when totally expended by multiple hits, the thick front wall of the blocks can still perform as simple spaced armour. In effect, the armour still provide a respectable amount of protection even if it is hit in the same area twice in a row, certainly still enough to immunize the T-62 from the shaped charge warhead of the less advanced versions of LAW rockets to the frontal arc. Going by steel thickness alone, an expended block and the main armour will still be too thick to be defeated by an M72A3 LAW from 1977.
Overall, "Brow" armour on the T-62M can be viewed as a case of "too little, too late". Portable threats such as the 105mm M40 recoilless rifle (400mm penetration), LAW, Carl Gustav (400mm penetration), and the anaemic M47 Dragon (450mm of penetration) were effectively neutered, and "brow" armour can be considered very successful as a low cost equalizer of the status quo in that context. However, the ITOW was just around the corner by the time the T-62M was introduced, and it would have been able to defeat this new armour with relative ease from the front. "Brow" armour could not change the status quo of the T-62 against opposing tanks given the relatively recent introduction of 105mm APFSDS ammunition, so even if it could offer full protection from 105mm M456 HEAT and M392A2 APDS and possibly M735 APFSDS, the T-62 could still never truly achieve the level of protection of the latest T-72, T-64 and T-80 tanks. This, combined with the general obsolescence of the chassis itself, meant that any further potential for the T-62 was exhausted. Nevertheless, these obsolete tanks reigned supreme in Afghanistan in the absence of a serious anti-tank threat, and it was there that "brow" armour proved to be the difference between life and death.
"Brow" armour was not exclusive to Volna-equipped T-62Ms, or even to the T-62M in general. Many T-62s have been seen in Afghanistan with "Brow" armour and sideskirts, but no other upgrades. The lack of a laser rangefinder is a dead giveaway for the tanks below:
This is expected, as "Brow" armour is an applique armour kit that is intrinsically compatible with the T-62. There is nothing to limit the installation of it to older versions of the T-62. In fact, it was not uncommon to see a pre-1972 model T-62 equipped with "Brow" armour in Afghanistan, as field technicians did the best they could to armour up the army's valuable armoured assets with whatever they had. The photo below shows an early model T-62 (distinguished by the loader's hatch) equipped with "Brow" armour leading what appears to be a tank platoon. The second tank in the line is a T-62M, as we can see by the smoke launchers on the right side of the turret.
The photo below shows another early model T-62 with "Brow" armour.
And the photo below shows another one in a partially hull down position.