Early Composite Armour

Lately Airborne Combat Engineer has been on fire, posting several articles a day, many of them quite interesting. The latest one which caught my eye is this commentary on the latest U.S. Navy SinkEx. It seems they discovered that .50cals and 20mm cannons are capable of rapidly disabling destroyers.

Well, that is hardly surprising, and it reminds me of a story I read once about World War II. I tried to find more corroborating information on the story by searching the internet, but found little. It goes something like this: at some point during that conflict, fairly early I recall, .50 calibre machine-guns began replacing .30 calibres on fighter aircraft. The .30s just didn’t have the power to penetrate the armour of other modern fighters sufficiently—it’s depressing when you unload your entire store of ammunition into another fighter and it’s still flying. That someimtes happened even with .50cals and bigger, but that’s a story for another day.

Well, this move had other effects and the pilots soon realized they had real power against ground targets too. The .50cal bullets would easily penetrate trains, many buildings, and yes—you guessed it—ships. A favorite tactic was to rake the superstructure of a lonely destroyer, frigate, merchantman or similar with concentrated fire. often crippling the ship. Smaller ships could be quite easily sunk.

This doesn’t mean the modern exercise was unnecessary. They were looking into whether they could specifically disable a ship without sinking it, using .50cal or 20mm fire. But as this was often the outcome of strafing runs during WW2, if for no other reason than the command structure of the ship was shredded, it was to be expected.

And this brings me to my interesting story. Modern battle tanks have what is known as “composite armour”. The exact design of this armour is typically classified, but it is fairly well known that it’s often made of layers of ceramic with other substances embedded or surrounding it, likely including aluminium, steel and kevlar. The most famous is the British “Chobham” armour used in tanks such as the Abrams. But composite armour has been around since, and before, the Second World War.

Because strafing aircraft were so effective when targeting a ship’s superstructure, and because steel was relatively scarce, various countries experimented with alternatives for armouring their ships. The Germans fitted concrete around the steel of their superstructures, while the British developed a mixture of bitumen and pebbles they called “plastic armour”. The British armour turned out to be superior to the concrete type. Of course, concrete is used extensively as armour on land structures such as pillboxes, and if thick enough it will definitely protect against .50cal fire. But there was a limit to how thickly they could apply it outside the steel of the ship. So the boffins came up with the idea to set the material with lots of large pebbles in it. When hit by bullets, the pebbles would rotate inside the bitumen matrix, robbing the projectiles of much of their kinetic energy, and also deflecting them. Most bullets would no longer penetrate the composite armour, even though they could penetrate a similar thickness of plain bitumen. While modern composite armour is likely far more advanced, I bet it relies on much the same principle.

There were also ships made entirely from concrete (again because steel demand exceeded supply) but that’s a whole other story.

Update: Thanks to reader Bill Befort for pointing out to me that the armour was set in bitumen, not concrete, and giving me the name and link!

—posted by Nicholas.


  1. The whole issue isn’t a new one. The pure reason why todays naval (war)ships are so vulnerable to both .50cal and 20mm is a simple one: cost. The more you armor up a ship, the heavier it becomes, the more expensive it becomes to push it through the water. Also, todays warships are really a product of the Cold War where the name of the game was Submarine hunting and not terrorist/pirates a-wacking. Ships were designed to be fast and quiet from the keel up. A notable exception were the Soviets, who did armor their ships (at a cost of some other equipment) and the old US Re/Decommissioned Battleships and the USN Arleigh Burke class of destroyers. Also, no machinegun toting aircraft (or small boat) would come into range during a conflict; triple layer missile/gunshields would give any Kamikaze-wannabe a seriously bad hair day (Phalanx or Goalkeeper CIWS anyone?). The main threat during and shortly after the Cold War was missiles; the Brits found that out during the Falklands War and the US after the frigate USS Stark was hit by an seaskimmer. Point of interest: both the Brits and the USN got hit by the French Exocet seaskimmer – ships and missiles all from NATO allies (…) Gotta love the French kiss. Marcus

  2. Right, but I guess this means—among other things—that port security is damn important. It can’t be hard to sneak a .50cal up near a warship that’s in dock and open fire if port security is lax, and it could do quite a bit of damage. But then, since the USS Cole incident, we knew that.

  3. That, and maybe it makes sense to start building some ships with more armour now. Especially those expected to operate in a littoral environment. Or else, give them enough agile firepower to easily take out small agressor craft. But it would be better to have both if possible.

  4. Shipmates, Interestingly enough, the Sheffield sank in heavy seas whilst being towed from the area. Although she was struck by the Exocet, the warhead failed to detonate. Damage to Sheffield was a result of excess fuel in theExocet’s tank bursting into flames and igniting the vinyl material used as a cost-saving material inside the vessel. The majority of her casualties were from thick toxic fumes. Additionally, the missile managed to cut the single firemain which serviced the fire-fighting equipment, thus slowing the response to the flames. Both the vinyl insulation and the single firemain were a result of English Navy cost-cuting methods used in shipbuilding, and both resulted in unnecesary loss of life, and eventually the ship itself. Respects, AW1 Tim

  5. Anything which gives off significant volumes of toxic fumes during combusion should probably not be used on a combat vehicle. Didn’t the M1 Abrams’ fibreglass fuel extractor have a similar problem?

  6. Cost was the 1st excuse why ships no longer were armored. The theory being that the cost to armor a ship to withstand attacks was huge, not only in the actual metal/construction costs, but in the maintence and government subsidies costs needed to maintain the specialized steel mills. So the thoery was use missiles and ECM to defend the ships. Once we lost the capability to produce armor. All we have is the electronic defensese. Now on modern ships the cost of the hull and superstructure is a minor component. The added cost to minimally armor a ship to survive small arms fire would be rounding a error in the greater scheme of things. I predict that this will become a priority once some Somali pirate sinks or disables a billion dollar destroyer.

  7. I remember being on holiday visiting relatives in the states. Isn’t there somewhere on the NJ coast a concrete ship that is half submerged near the shore? I just recall this as I was quite young at the time. As I recall it was WW1 era. I think I remember there being a slipway on the beach aswell, but I could be mistaken. It was indeed a long time ago.