Uranium is 'pyrophoric': at the point of impact it burns away into vapour, so the projectile stays sharp. When a tungsten rod strikes armour, it deforms and mushrooms, making it progressively blunter. The other metal used for anti-tank rounds is tungsten, which is also very hard and dense.

DU is almost twice as dense as lead, making it highly suitable. The denser the projectile, the harder the impact for a given size. A faster shell does not necessarily go through more armour, but, like a pebble thrown into a pond, it makes a bigger splash.Īrmour penetration is increased by concentrating the force of a shell into as small an area as possible, so the projectiles tend to look like giant darts. Metal flows like putty, or simply vaporises. When metal meets metal at five times the speed of sound, hardened steel shatters like glass. To understand why DU makes a good anti-tank weapon you have to enter the Alice In Wonderland world of high-energy collisions. It is a poisonous heavy metal like lead or mercury, but only slightly radioactive.

U-235 is used in reactors and atomic weapons once it is extracted, the rest is depleted uranium (DU). In its native state it is a mixture of highly radioactive uranium-235 and less active U-238. Metallic uranium occurs naturally in tiny quantities.

Force behind a tank shell