The deadliest weapon of the 21st century

Forget about nuclear missiles, the decisive weapon of the 21st century is the car bomb. All you need is a battered old car, a couple of hundred pounds worth of homemade explosives and you can attack a superpower, start a civil war or just blow up your own government.

When people think of car bombs, they think of insurgents, splinter groups, the Middle East. But surprisingly, the car bomb was invented in America.

The first car bomb, actually a horse-and-cart bomb, was planted on Wall Street on September 16, 1920. Packed with shrapnel, the bomb exploded without warning into the crowd, killing 38 people. The bombing was the work of Italian anarchists.

The Wall Street bomber was never caught. But Wall Street was the blueprint for all future car bomb attacks. Yale historian Beverley Gage says: "The wagon blows up

and the thing that the investigators found was that no-one actually noticed the driver. Having an old wagon around, a peddler's cart, just was not unusual." And that's the deadly nature of the modern car bomb. A car bomb is invisible in everyday traffic but can pack the same explosive punch as an F-16 fighter bomber.

The modern car bomb was also invented in America - by Karl Armstrong, a 22-year-old college drop-out and Vietnam War protester.

Armstrong blew up his Wisconsin university in 1970 with a 1.5-tonne car bomb as a protest against the Nixon administration's war policies. Shockingly, Armstrong got the recipe for the bomb in Encyclopaedia Britannica - under 'Explosives'. But there was another twist. Armstrong bought the base material for his bomb - ammonium nitrate, farmers' fertiliser - from the local hardware store for $200. Just by adding diesel fuel, he created the perfect homemade terrorist weapon - an ammonium nitrate fuel oil (ANFO) bomb.

Armstrong's act of serendipity would have appalling global consequences that would spread across the Atlantic to the Troubles