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 in Ireland. The Provisional IRA would plant hundreds of car bombs, which like Armstrong's, came from ammonium nitrate. Every farm in Ireland used the same fertiliser. The IRA's bombs got bigger and stronger.

The biggest IRA bomb of all exploded at 10.27am on Saturday April 24, 1993 when a 3,500lb ANFO truck bomb went off in Bishopsgate in the City of London. The bomb cost the IRA around £500 to make yet cost the British taxpayer £1bn in insurance claims. As bomb disposal officer Mike Coldrick said: "Amazing - it's a real bang for bucks." The Troubles ended soon afterwards and a peace deal was hammered out.

In the right place, and with the right amount of explosives, car bombs really can change history.

The third and most deadly car bomb is the one detonated by the suicide bomber. The first suicide car bomb attack on a Western target was at the US Embassy in Beirut in April 1983 when six of my close colleagues in the CIA were killed. When I was stationed in Beirut, suicide car bombs were a daily risk. It was a lesson we should have remembered before invading Iraq.

Iraq was hailed as the perfect blitzkrieg. A country the size of California seized in less than three weeks, at the cost of just 139 men. Until car bombs. In Iraq's cities the car bomb evened the odds, tilting the balance of power away from the might of the US Army in favour of the insurgents. For US troops, every car was a potential artillery shell ready to blow up in their faces. Today, the overall death toll in Iraq stands at more than one million people: 200,000 of these died as a direct result of car bombs.

The car bomb allows the poorest guerrilla organisation to match the strongest military. Even the White House and Downing Street have turned into fortresses because of the threat of the car bomb.

Truly, in its make-your-own simplicity and invisibility in traffic, the car bomb is the deadliest weapon of the 21st century.
Robert Baer presents 'Car Bomb' on Channel 4, Sunday July 27 , 7pm ·