During the later years of WWII, German tanks were delivered to the field with a strange rough texture on top of their armor. You’ve likely seen this and wondered what it is and what its for.

This material is called Zimmerit and was meant to defend against mines. Despite its lengthy and labour intensive application process, it proved to be almost entirely pointless. It is now regarded as another example of Germany’s odd priorities during the war.

The creation of Zimmerit was a direct countermeasure against anti-tank mines – specifically magnetic mines.

As implied by the name, these mines would be stuck onto a tank’s armor plating by infantry outside the vehicle. It was dangerous work. If a mine was successfully attached to a tank, there was little a crew could do. If they even knew it was there – to prevent its detonation.

Zimmerit attempted to reduce the usefulness of anti-tank mines. It increased the distance between the armor and the magnets within the mine. In theory, this would prevent a mine from adhering.

The Germans introduced the Hafthohlladung anti-tank magnetic mine in 1942. This 3 kg weapon contained a shaped charge that could punch through up to 140 mm of steel. This being over three times the thickness of a Sherman’s side armor.

It was attached to the target via three strong magnets at the base of the mine. Not only did these serve as the method of adhesion. They also acted as spacers that kept shaped charge at the optimal distance from the armor (allowing the jet of molten metal to form).

As they were magnetically attached, these types of mines made angled armor useless. And therefore only had to tackle the raw plate thickness.

Germany produced over half a million Hafthohlladung mines during the war. Most of them being replaced in the latter stages of the conflict by the Panzerfaust.

However when they were first introduced Germany feared that the weapon could easily be copied by their enemies. So they set about developing countermeasures to prevent enemy mines from working.

This research culminated with Zimmerit.

As mentioned, the aim of Zimmerit was to increase the distance between the steel armor and the magnets. As magnetic strength decreases rapidly over distance. To do this, the Germans experimented with a number of physical barriers applied over a tank’s armor.

They tried layers of concrete, thick paint and even ice, but none of these were found to be practical.

Eventually the company Zimmer & Co concocted a putty-like substance that dried to a rock-hard finish. It consisted of pine crystals, benzene, barium sulphate, zinc sulphide, PVA glue, saw dust, pebble dust and ochre.

Once mixed the paste was applied with a trowel. Each vehicle that received Zimmerit had specific instructions for where it should be applied. To save time and resources, Zimmerit was usually only applied on surfaces in reach of infantry.

It was not applied to areas like hinges and grilles. And other areas that a magnetic mine would not work well on, like lights and side skirts.

A finished layer of Zimmerit was 6 mm thick, and had to be applied in a very particular way. First, a 2 mm thick layer was placed on the vehicle and left to dry for four hours.

This first layer was then hit with a blowtorch to accelerate the hardening process and to burn off excess moisture.

Once this was done, the final 4 mm was applied. At this stage the distinct pattern was pressed into the coating and it was once again blasted with a blowtorch. The benzene in the mixture produced intense fires when it met the blowtorch. However. without this complex process, the Zimmerit coating would have taken 8 days to dry.

The ridges in the coating increased its thickness without adding more material. This was a good thing too. As a 200 kg of Zimmerit were used on a Tiger, while a Panzer IV required 100 kg.

The patterns vary widely from simple lines to zig-zags to waffle shapes. The exact type depended on who applied it and to what vehicle.

For its intended purpose Zimmerit worked well. However there was one major flaw in the entire magnetic mine defense system. It was only the Germans used magnetic mines on any appreciable scale.

This meant the expensive, time consuming process to proof tanks against magnetic mines was a complete waste of time.

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In September 1944 Zimmerit was discontinued after rumours circulated that the coating caught fire when hit. Although the Germans proceeded to debunk this theory. Zimmerit was never ordered back into production, likely because there was no need for it.