In the German armed forces of World War II, what was "Zimmerit"?

”Zimmerit” was a paste-like coating used on German armoured fighting vehicles (AFVs) during World War II. It produced a hard layer covering the metal armour of the AFV, preventing magnetically attached anti-tank mines from sticking to the vehicle. It took its name from the Berlin chemical company that developed it, Chemische Werke Zimmer & Co.

The way it worked was that the coating formed a barrier that inhibited direct contact of magnetic mines with metal surfaces of vehicles. The magnetostatic field decreases rapidly with distance and the the non-magnetic coating holds the magnet of the mine too far from the steel of the vehicle for it to adhere to the target. The coating was normally ridged to increase the distance between the magnet and the armour even further. The mixture, a kind of thick putty, was applied to the AFV in the factory, patterned, and then hardened with blowlamps. There were many variations seen in application designs, mostly related to the factory producing each type of AFV.

There were two very odd things about the deployment of the expensive coating kjnown as ”Zimmerit.” First, Germany was almost the only country to use magnetic anti-tank mines, so it is not clear why the Germans would spend so much money protecting against them. Second ”Zimmerit” was left off AFVs later in the war due to a concern that the material could catch fire when hit; but this concern was known to be unfounded.