Military Review

Gravel against a projectile. Experimental attachment armor for the M4 tank (USA)


Serial M4A2 in the museum. On board, the factory reinforced armor is visible in the form of additional sheets covering the stowage.

The American M4 medium tank had a fairly powerful armor, but it did not protect against all current threats. Since a certain time, several types of hand grenade launchers have become a serious problem. In this regard, attempts were regularly made to strengthen the standard armor with various overhead elements. One of the results of such work was the first American set of additional combined armor with a non-metallic filler.

Threats and answers

On the tanks M4 of the first modification, the frontal projection of the body had a thickness of 50,8 to 108 mm. The slope and curved shape of the parts provided a certain increase in the level of protection. Subsequently, the upper frontal part became thicker - 63,5 mm. The side projection in all modifications was protected by 38 mm of armor. The forehead of the early turret was 76,2 mm thick, while later hoods were protected by 89 mm armor.

The tanks were protected from bullets and shrapnel, as well as from small and medium caliber artillery. At the same time, the main German-made tank guns pierced the frontal armor of the hull and turret from at least hundreds of meters. In 1943-44. American tankers had to face a new threat in the form of rocket-propelled grenade launchers, which, upon a successful hit, confidently pierced the armor and hit the crew or internal units.

Experienced M4 with a set of overhead modules

Initially, the tankers tried to fight the new threat on their own. The armor was hung with caterpillar tracks, sandbags, boards and other "overhead additional booking". For obvious reasons, the effectiveness of such funds left much to be desired, and therefore the search for a full and efficient additional protection began.

HRC compositions

The US Army Department of Armaments launched new research in mid-1943 and continued it until the end of the war. First of all, various options for overhead armor blocks were considered, differing in steel grade, thickness and configuration. In addition, the possibility of using alternative materials was studied, incl. partial rejection of metals.

Replacing armor steel with other materials, in theory, made it possible to obtain the same level of protection with a significant reduction in weight - or to increase protection without increasing weight parameters. The search for the optimal compositions of such armor continued for a long time. Tests of finished samples began only at the beginning of 1945.

To enhance the protection of the tank, it was proposed to hang metal boxes filled with unusual "plastic armor". The first version of this "armor", designated HRC1, was a mixture of 50% aluminum filler and a binder - 40% asphalt or pitch with 10% wood flour. The second track, HRC2, was much simpler and cheaper. It consisted of 80% quartz gravel. The stones were glued together into a single structure using a mixture of 15% asphalt and 5% wood flour. It was planned to pour the mixture into a thick-walled aluminum box with fasteners for installation on a tank.

Gravel against a projectile. Experimental attachment armor for the M4 tank (USA)
The hull's forehead had only regular armor

HRC compositions differed from armor steel in lower hardness and higher toughness, as well as significantly lower density. It was assumed that a cumulative jet or an armor-piercing projectile, passing through an overhead block with aluminum walls and "plastic armor", would lose most of its energy, and the rest would be extinguished by the tank's own armor. In addition, the abrupt transition between different media should have caused additional loads on the projectile or jet.

Based on the results of preliminary tests with shelling of experimental modules, the HRC2 composition was considered more successful. The gravel-based mixture combined reasonable weight, high protection characteristics and low cost of production. All further work was carried out using this composition only.

Tank with blocks

Having chosen the optimal "plastic armor", the Department of Armaments began to develop a set of attachments for the serial M4 tank. At the same time, the fundamental possibility of creating similar products for armored vehicles of other types was not excluded. In fact, the modifications of the new armor had to differ only in the number and shape of individual modules.

It was proposed to build additional protection for the tank from separate elements of different shapes. Each such block was a box made of aluminum with walls and a bottom 25,4 mm thick. An HRC2 layer 254 mm thick was poured between the walls. On the lids of the boxes, brackets were provided for hanging on the tank; matching hooks were added to his armor. The suspension was carried out using 12,7 mm steel cables.

The armor set for the M4 tank included six modules to protect the side projection. They had an angular shape, due to which they covered the combat and engine-transmission compartment. Seven blocks were proposed for the tower. Two were on the sides of the mask, two more were hung at the sides. The stern was covered with one wide module. The experienced tank did not receive additional hull forehead protection. Perhaps such elements would appear later.

The set of overhead armor made of aluminum and HRC2 for the M4 weighed 8 tons. The weight of the set of armor steel with the same protection characteristics would exceed 10-12 tons. However, in this case, the armored vehicle experienced serious loads.

Gravel on trials

A prototype set of new armor was made only in the fall of 1945. At the same time, a prototype based on the serial M4 was tested at the Aberdeen Proving Ground. The main focus during the tests, for obvious reasons, was on enhanced protection.

During the shelling tests, it was found that RPzB. 54 Panzerschreck and Panzerfaust 100 (declared penetration 200-210 mm) are capable of damaging the combat module or even penetrating it, but after that they do not threaten the tank's armor. The turret modules successfully coped with the shelling, while the side hull blocks made their way several times - but without hitting the tank.

View from above. The means of fastening the blocks to the tank are clearly visible

Different results were obtained when firing with armor-piercing shells of caliber up to 76 mm. The HRC2 module absorbed some of the projectile's energy, but the rest was enough for a strong blow to the armor. The level of protection against kinetic threats turned out to be significantly lower than that of a hinged steel module of the same mass. In addition, the suspension system of the modules was criticized - under fire, the cable could break, and the tank lost a whole block of armor.

Reserve for the future

Hinged armor based on aluminum and a mixture of HRC2 in the course of independent tests and tests on the tank, as a whole, proved to be good. She successfully solved her main task, sharply weakening the power of the cumulative jet, although the effectiveness against sub-caliber projectiles was insufficient. With all this, the armor was quite simple and cheap to manufacture. Installing and replacing damaged blocks was also not difficult.

Nevertheless, the original overhead modules were not accepted into service and put into series. The main reason was the end of the war and the processes that followed. The US Army no longer needed emergency measures to strengthen armored vehicles. In peacetime conditions, it was possible to do a more thorough study of the issue of overhead armor, or even start the development of a completely new tank, which initially had the necessary level of protection.

Attached modules with non-metallic filling did not enter service, and the main ideas of this project were forgotten for some time. Further development of the protection of American tanks was associated with the improvement of homogeneous armor. However, later the potential of this direction was exhausted, and a new increase in the level of protection of armored vehicles was needed. And now already well-known ideas have come into play - both overhead modules and combined systems, incl. with non-metallic elements. In the future, both solutions became widespread and became the de facto standard for modern combat vehicles.
Photos used:
RP Hunnicutt. Sherman. A History of the American Medium Tank, Wikimedia Commons
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  1. sen
    sen 4 January 2021 06: 38
    The first version of such "armor" under the designation HRC1, was a mixture of 50% aluminum filler and a binder - 40% asphalt or pitch with 10% wood flour

    There is a more interesting option. The binder is aluminum, the filler is "pieces" of ceramics based on aluminum oxides. Since such ceramics contain aluminum, they will have good adhesion to the binder (adhesion).
    1. Sergey M. Karasev
      Sergey M. Karasev 4 January 2021 11: 29

      It will be correct - adhesion.
  2. The leader of the Redskins
    The leader of the Redskins 4 January 2021 07: 49
    I thank the author for the interesting material. It's not trivial. Personally, I have not read about these experiments.
  3. Vladimir_2U
    Vladimir_2U 4 January 2021 09: 10
    Modular overhead armor as it is, at those possibilities, and at the same time quite expensive, but this is the same the Americans could then afford. Ours worked out the concrete additional armor of the T-34, which turned out to be a monster.
  4. Sergey M. Karasev
    Sergey M. Karasev 4 January 2021 11: 33
    Yeah ... We would have as much aluminum in WWII as the Americans had ... Otherwise, until the end of the war, most aviation had a "mixed design" at best. request
  5. Free wind
    Free wind 4 January 2021 12: 24
    From the article I did not understand whether the Americans are so cowardly, or whether we are brave. The trains were also protected by additional booking. Railway platforms were lined with sandbags - earth around machine-gun points, they jokingly called train blindies. Armor does not bother anyone if it helps to survive. On the T-62, additional booking looks quite powerful. They defended their lives, and they did the right thing.
    1. Free wind
      Free wind 4 January 2021 20: 13
      Haven't you seen the T-62?
  6. Saxahorse
    Saxahorse 4 January 2021 19: 34
    During the shelling tests, it was found that RPzB. 54 Panzerschreck and Panzerfaust 100 (declared penetration 200-210 mm) can damage the combat module or even penetrate it,

    Such formulations are confusing, however. If Panzerschreck can still be called a rocket launcher, then Panzerfaust is not a "rocket launcher". Rather a recoilless gun. :)
  7. voyaka uh
    voyaka uh 4 January 2021 23: 08
    The merkava is all covered with curtain panels like a turtle.
    The photo shows how the kumm jet tangentially shattered the panel on the tower "into chips".
    Overall, the curtain panel system works decently, stopping
    even 150 mm ATGMs, although not 100%. KAZ complements them.
    1. Intruder
      Intruder 5 January 2021 14: 37
      our gloomy Soviet genius also had similar ideas: 1) the idea of ​​a two-barrier armor (80 mm steel + 140 mm fiberglass), originally proposed for the T-64, was replaced by a design with a 20-mm back plate (back support) while reducing the thickness of fiberglass up to 105 mm. This scheme (80 mm steel + 105 mm fiberglass + 20 mm steel) was chosen as the main one both in the further production of T-64 and T-64A, as well as machines developed on its basis - T-72 and T-80.
      2) for the tower:
      - steel armor casting with ultraphoric inserts with an initial base horizontal thickness equal to 420 mm with an equivalent anti-cumulative protection equal to 450 mm;
      - cast tower, consisting of a steel armor base, an aluminum anti-cumulative jacket (poured after casting the steel hull) and outer steel armor and aluminum. The total maximum wall thickness of this tower is ~ 500 mm and is equivalent to anti-cumulative protection of ~ 460 mm.
      Serial production of towers with ceramic filler (lined corundum balls and baskets for their installation in a casting mold) for T-64A and T-64B tanks continued for 15 years - until December 27, 1987, when the last T-64BV left the assembly shop.
  8. kagulin58
    kagulin58 8 March 2021 11: 26
    And these tanks apparently had such a detail as a protection! As much as 38 mm armor! Drunken delirium of the author.
  9. Mikhail3
    Mikhail3 20 March 2021 15: 53
    As far as I remember, one of the very successful versions of our anti-cumulative protection and protection against RG projectiles is precisely the ceramic elements connected by an elastic compound. When a projectile hits, the ceramic elements are displaced towards each other, taking the projectile cone "in a vice". Then they begin to collapse, destroying the projectile itself, and absorbing its kinetic energy. The cumulative jet is also extinguished by the fact that it does not begin on the surface of the main armor, and even is crushed by ceramics.
    Apparently, the American version did not show all the possibilities due to an unsuitable compound, as well as due to the fact that loose gravel was used. I did not know that such experiments were carried out already at 43. That is, our version was created on the basis of the American ...