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.