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