Zimmerit

Shortly before the launch of the USS New Mexico, a modern fast attack, nuclear submarine, the Captain and First Officer made a goodwill tour of New Mexico.  As part of the tour, they came to my class on the History of Naval Warfare at Enema U.  It was a great talk and, in hindsight, I realize that I probably did not thank the US Navy enough.

At the end of his talk, the boat’s Captain asked if there were any questions.  My class was a little shy, so I primed the pump by asking what the top speed of the sub was expected to be.  The Captain smiled and said, “A little under 35 knots.”

I expected that answer since, according to the US Navy, every large ship currently commissioned goes “A little under 35 knots.”  Supposedly, even modern American destroyers are slower than their counterparts in World War II.  The true top speeds of American warships are absolutely classified and only the US Navy and every one of our enemies know the truth.   

I smiled back and asked the question that I was really curious about.  “Will the USS New Mexico be covered with anything special?”

Once again, the boat’s Captain smiled and replied, “Just anti-fouling paint.”

We both knew he couldn’t say more.  I have no idea exactly what subs are really covered with, but it is a hell of a lot more than anti-fouling paint.  There are some kind of noise deadening rubber tiles that make the sub harder to detect by both radar and sonar, but exactly what they are made of is classified.  

Classified coatings for military use are not exactly new.  In 1917, during World War I, the British Royal Navy introduced “dazzle” camouflage, using complex, high-contrast patterns to confuse enemy targeting.  Since there was no real evidence that it worked, it was tried briefly by both Great Britain and the United States in World War II.  To this day, there is no clear consensus on whether the strange paint job really worked, though there is some anecdotal testimony that torpedoes missed the dazzle ships because submarine captains couldn’t stop laughing.  (I wonder if it has been tried on cars to confuse traffic cops?)

In the 1970’s the US started covering military vehicles with something called CARC (Chemical Agent Resistant Coating) that supposedly made vehicles exposed to chemical agents easier to clean.  And we all have heard about the modern coatings that make aircraft harder to see on radar.  There is, however, an earlier special coating for tanks that you have probably never heard of: Zimmerit.

During World War II, Germany was concerned that the Allies might target their armored vehicles with magnetic bombs.  Remember the scene in Saving Private Ryan when Tom Hanks destroys a Tiger tank with a “sticky bomb”?  (Well, technically the tank was a Russian T-34 with wood and paper mâché added to make it look like a Tiger tank, but let’s not be picky!)

According to the movie, a sticky bomb was a plain GI sock crammed full of explosives with a simple fuse, with the sock then covered in axle grease.  An incredibly brave soldier would light the fuse, run up to the enemy tank, slap the improvised mine against the steel side of the vehicle, then run away before the bomb blew up.  There was, of course, no such bomb used in World War II.  The British had developed a No. 74 Sticky Bomb, but it was nitroglycerine in a glass container that could adhere to the side of an enemy vehicle with adhesives.  The weapon was ineffective and far better results could be achieved with other anti-tank weapons like the American bazooka or the British PIAT.

There was a magnetic mine used during World War II, the Hafthohlladung (or as it was more commonly called, the Panzerknacker or “Tank Breaker”).  Developed in 1942, this was a shaped charge that was attached to three strong horseshoe magnets.  A soldier could place one against the side of an enemy tank, pull the firing pin, then run like hell before the 4.5 second fuse detonated the bomb.  Needless to say, this was a difficult getaway to accomplish.

Pondering this led to the Germans worrying about magnetic explosives being placed against the sides of their tanks.  Their response was the development of zimmerit—a thick plastic-like foam mixed with sawdust that was applied in inch-thick ridges to the sides of their tanks, hardened with a blowtorch and left to dry.  The foam material was mixed with a yellowish-brown ochre, making the tanks look like they had been covered with thick cooked waffles.

The idea was that the thick zimmerit coating would prevent the magnetic bombs to be close enough to the tank for the magnets to work, so they would simply fall off the side of the vehicle.  The process of applying the zimmerit at the factory took several days, and despite the desperate need of more tanks at the front line, Germany continued to apply the protective foam on its armored vehicles from December 1943 to September 1944.

You would think that the reason that the Germans stopped using zimmerit was because they finally noticed that Germany was the only country using magnetic mines against tanks.  Or maybe it was that Germany realized that, since the Allies had developed projectile anti-tank weapons, the likelihood of someone attempting to physically place a mine onto a tank (outside of Hollywood) was highly unlikely.  Those are both good possible explanations, but neither is the reason the Germans stopped using zimmerit.

Germany was afraid that the new Allied projectile weapons (like the American bazooka) might set fire to the zimmerit…So, they stopped using it.

British tests after the war discovered that it was all but impossible to ignite zimmerit!