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Weight

  25 tonnes (55,000 lb) Length 7 metres (23 ft 0 in) Width 2.7 m (8 ft 10 in) Height 2.1 m (6 ft 11 in) Crew 2 (Commander, Driver)

 

That's the Terrex 1. The Terrex 2 is according to the official factsheet 9.03 feet (2.75 metres) tall; this might include the RWS. The Terrex 3 is based on the Terrex 2 hull with stronger suspension.

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It's not resin, the add-on plates are made of steel, but covered with rubber. Supposedly this has something to do with hardness and shattering (it is supposed to be very high-hardness steel according to the patent from the manufacturer).

 

The only reference to ERA I can think of is the mounting mechanism. The steel bolts can be recessed a bit and has a thick rubber block at the base. This is claimed to work like a coil-spring, but is indepent of impact angle (whereas a coil spring will fail to work at certain angles). If this actually provides any noteworthy amount of protection needs to be debated though, I have seen different opinions on this.

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It's not resin, the add-on plates are made of steel, but covered with rubber. Supposedly this has something to do with hardness and shattering (it is supposed to be very high-hardness steel according to the patent from the manufacturer).

 

The only reference to ERA I can think of is the mounting mechanism. The steel bolts can be recessed a bit and has a thick rubber block at the base. This is claimed to work like a coil-spring, but is indepent of impact angle (whereas a coil spring will fail to work at certain angles). If this actually provides any noteworthy amount of protection needs to be debated though, I have seen different opinions on this.

 

Do you know if the add-on plates are single layer or multi-layer?  I had seen a computer simulation of multi-layer plates which purported to be a model of the Leo 1A1a1 add on armor kit that showed a bunch of thin layers of steel with air gaps between.

 

But this was just a computer model, and may have had nothing to do with reality.

 

Put me down as skeptical that mounting armor on any sort of spring would meaningfully effect the penetrator.  Especially if it's HEAT.

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So, it is pretty much a very high hardness steel plate, that is covered in rubber to avoid the steel from completely shattering. And placed on a rubber padding to dissipate the energy of the incoming projectile? The rubber padding would at least reduce the G-forces experienced by the steel plate. As for as I understood.

 

So how much added protection would this be?

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So, it is pretty much a very high hardness steel plate, that is covered in rubber to avoid the steel from completely shattering. And placed on a rubber padding to dissipate the energy of the incoming projectile? The rubber padding would at least reduce the G-forces experienced by the steel plate. As for as I understood.

 

So how much added protection would this be?

It probably can help with HE rounds and fragments, probably against early HEAT, but nothing more.

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The protection should depend on location, type of ammunition and angle of impact.
 
fotocd_01.jpg
 
Most of the Leopard 1 turret's frontal profile is covered by the gun mantlet. This has a thickness of something about 150-160 mm and is reinforced by a spaced steel add-on (not covered in rubber) in the Leopard 1A1A1 upgrade and follow-up versions. I don't know the exact thickness, but it appears to be some 40-50 mm thick. Afaik it still uses a similar rubber-padded bolt design as the rest of the applique armor. Together with the slope, this should lead to more than 220-250 mm steel along the line of sight.

leopard_c2_152_of_209.jpg

 

Above the gun mantlet, the frontal roof area is sloped at 23° and has a thickness of 45 mm. This equals 115 mm along the line of sight. The add-on armor includes the installation of five rolled steel plates here, which have a thickness of 25 to 28 mm and are backed by a 3 mm layer of rubber (so it's 25-28 mm rolled steel + 3 mm rubber + 45 mm cast steel; all at 23°)... together this should equal 179 to 186 mm of steel. It's not very much, but the corresponding sections of other tanks like the M60 and Chieftain are not much better armored, as it is too sloped for APDS and early APFSDS to penetrate.

 

The frontal turret armor has a thickness of 65 mm sloped at 30°, which leads to 130 mm along the line of sight. Here the rubberized high-hardness plates have an actual thickness of 45 mm - if we account the vertical and horizontal slope however, the thickness along the line of sight should increased to 100 - 120 mm... so the Leopard 1A1A1 has some 200 to 250 mm thick frontal armor (+ some empty space). We however don't know how thick the rubber padding is, how hard the steel is and how effective the space array is (and if the bolt design does actually affect protection)...

 

The US Army found that cast steel armor provides about 15% less protection than rolled steel armor; Soviet cast steel armor was supposedly 5 to 15% less effective than rolled steel armor according to "Soviet/Russian Armor and Artillery design practices". So if it wasn't for the rubber coating, we could clearly say that the spaced armor provides more protection per thickness (if we exclude the empty space) than cast steel armor - but unfortunately there is an unknown amount of rubber. High hardness steel can in theory increase the protection by factor 2 with modern alloys and manufacturing techniques:

 

725x530-armox-pure-steel-pure-evolution.

 

For the steel used on the Leopard 1 applique armor, there unfortunately is no data. The idea from Blohm & Voss described in the patent was that using the "rubberized plates mounted on bolts" design, steel alloys that cannot be welded or cast could be utilized. Paul Lakowski claimed in his armor basics document, that high hardness steel with 400 to 550 brinell hardness can provide 12 to 25% more protection per thickness. So in theory a 45 mm rubberized steel plate can provide protection equivalent to anything between 30-32 mm (assuming there is ~15 mm thick rubber coating) and 50 mm (assuming there is only 5 mm rubber and the steel is 25% more resistant than normal RHA) or more.

 

Last but not least, the armor is spaced; this can also affect actual protection. The Chieftian's 120 mm L15 APDS can penetrate 150 mm at 30° (300 mm) at 1,000 yards, but at the same range it defeats only a three layer spaced armor array with a combined plate thickness of only 115 mm (i.e. penetration is ~24% lower).

 

If we combine all of this, the Leopard 1A1A1's frontal armor might provide only 200 mm (or slightly less) steel-equivalent protection against APDS/HEAT or it might provide protection up to 300 mm (or slightly more) at the area's covered by the spaced applique armor. It all depends on too many unkown factors. According to German literature, the Leopard 1A1A1 is supposedly protected against smaller shaped charges like the RPG-7 or BMP-1 ammunition.

 

leopard_c2_149_of_209.jpg

 

The further the applique armor is located away from the front, the thinner it gets. The rear section of the turret sides is only covered by some 20 mm of armor.
 

 

In general the Leopard 1A1A1 turret is quite ambivalent; it might be extremely well protected for it's time or just below average.

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The US Army found that cast steel armor provides about 15% less protection than rolled steel armor; Soviet cast steel armor was supposedly 5 to 15% less effective than rolled steel armor according to "Soviet/Russian Armor and Artillery design practices". So if it wasn't for the rubber coating, we could clearly say that the spaced armor provides more protection per thickness (if we exclude the empty space) than cast steel armor - but unfortunately there is an unknown amount of rubber. High hardness steel can in theory increase the protection by factor 2 with modern alloys and manufacturing techniques:

 

 

 

 

Do you have a source for that?  That's much, much greater efficiency than I have ever seen cited for HHS.

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Well, you can see the graphic from SSAB (Swedish steel manufacturer) above. The ARMOX Advance steel provides twice as much protection as ARMOX 500T (hardness: 480-540 HBW) steel against 5.56 mm AP ammunition. It is probably not very applicable for tank armor, given the requirements for plate thickness (ARMOX Advanced can only be manufactured to a maximum thickness of 20 mm) and the different threats. SSAB supplies armor steel for vehicles such as the CV90, the Sisu Pasi, the Piranha III, the Boxer and the Leopard 2 (although the later two vehicles also utilize Thyssen-Krupp Secure steel). The US found ARMOX Advance and 600T to outerperform MIL-DTL-46100E steel (hardness 477-534 BHN) and MIL-A46099C dual hardness armor (hardness 601-712 BHN for the front plate and 461-534 BHN back plate).

 

French company Arcelor Mittal claims that the latest MARS 600 high-hardness steel provides twice as much protection as MARS 190 (hardness about 400 BHN) against 7.62 mm Ball ammunition.

 

Jane's reported that the Leclerc uses a three-layer steel, which can provide up to 1.8 times the protection of normal RHS. Supposedly similar two/three layer steel combinations have been utilized on the AMX-32/40, the Leopard 1A3/1A4, the Osorio tank and the Leopard 2 aswell... probably also on the Challenger tanks.

 

The difference between the Leclerc's steel arrangment, Armox Advance and the old Leopard 1's applique armor, is that the more modern steels are designed for welding, while the Leopard 1's applique armor is designed to utilize non-weldable steel alloys.

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I suspect that the improved efficiency vs. M193 ammunition is a special case.

 

M193 is known to cause adiabatic shear, or plugging failure in certain grades of steel at short range due to its very high velocity.  In order to have drastically better protective efficiency vs. M193, the steel would have to be just different enough to not suffer from that failure mode at that particular velocity.  There are some steels where M193 will cause plugging failure, but M855, which has a lot more sectional density and a steel core, will not despite being only slightly slower.

 

So I really doubt that this could be generalized to a 100% increase in TE.  10-15% improvement for high hardness steel, 20-30% improvement for dual hardness steel laminate (HHS strike face with more ductile backing plate) and 50% improvement for triple hardness laminate (soft hard soft) are on the order of what I've seen published and claimed.  The 80% claimed for the triple hardness steel laminate seems high, but it's in the same ballpark.  A generalized 100% improvement over RHA for a high hardness homogenous steel is bonkers and absolutely completely out of line with what I've heard.

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I think your values are wrong and considerably understating the protective capabilities of high-hardness steel - at least against small calibre weapons such as assault rifles and machine guns.
 
The M193 might have it's problems, but not all sources claiming a higher thickness efficiency than 1.15 are based on testing with the M193 ammunition. The MARS steel was tested against French 7.62 mm Ball ammunition. IBD Deisenroth, German armor designer, tested ARMOX 500 high-hardness steel and their own high strength nitrogen steel P-900N3 against the Russian 7.62×54mm B-32 armor-piercing round: ARMOX 500 required 16 mm at 0° to stop the AP ammunition, while the P-900 steel from IBD required only 11.5 mm - that's a 39% better protection per thickness compared to SSAB's high-hardness steel (which already is a lot better than RHA).

 

Your values might have been valid at some point of time (1970s, 1980s?) to reflect the protective performance of steel, but hardness and strength of modern alloys has increased steadily. As noted by Showater et Aal. in 2008, modern high-hardness steel with a hardness of over 650 BHN and a tensile strength of 2.0 to 2.25 GPa provides 10-20% higher values for V50 (velocity required when fired at 50 metres distance to penetrate the armor) against 0.3 and 0.5 cal armor-piercing ammunition compared to normal high-hardness steel (~500-550 BHN). According to R.M. Ogorkiewicz "Advances in armour materials" published in 1991, high-hardness steel with a hardness of 550 BHN provides 17% better protection against 7.62 mm AP ammunition than RHA with 380 BHN (which is a bit harder than usually cited and a lot more harder the cast armor of Leopard 1, M60, Chieftain and T-62). That was 25 years ago, hardness, elongation and strength of the alloys has been improved since then.

 

Interestingly Dr. Manfred Held proved in 1993 that high-hardness steel also provides more protection against shaped charges. Didn't know that before researching this topic a bit more.

 

On the Leopard 1 (and on the MBT-70), high-hardness steel as part of the spaced armor was designed against the brittle tungsten-carbide and steel penetrators of anti-tank ammunition in the first place, which had a lot of issues with breaking and shattering against complex targets and high hardness plates.

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