Gerard Hanratty gave a step-by-step demonstration at the Old Bailey in London of how he made the devices.
Mr Hanratty, 38, denied that it was ever intended that the dummy bombs should contain explosives. Along with seven other men he denies plotting to attack six electricity sub-stations that link the National Grid to London.
He told the jury yesterday that his IRA unit intended to trick the electricity company into turning off the power. "The electrical impact would be total disruption in London. All the traffic lights would be out. It would result in chaos. All industries would be starved - rail, Tube and travel," he said.
He added that he thought the "brilliant" plan would have created "a political impact for John Major and the British government and make a fool of the ring of steel round London which stops the IRA entering the City".
The prosecution alleges Mr Hanratty was part of an IRA active-service unit which plotted to use bombs to destroy the electricity sub-stations.
Mr Hanratty described making 37 boxes containing electrical timing devices after arriving in London. He said that the authorities would have had no option but to deal with the boxes, placed in the sub-stations, as if they were real.
"Any bomb-disposal officer called to deal with such a device in the vicinity of 100,000 volts would have to turn the electricity off before. The result would be no electricity in London for however long it took to deal with the devices. It would take a minimum of hours - we felt they would be dealt with in a day and a half." He added that it was too risky to place explosives in the power stations.
He gave a demonstration in court of how he made the devices and said that various clues were to have been left to confuse bomb-disposal experts, including wooden dowels used for arming and safety pegs, which would have indicated the devices were fully armed.
He said the IRA had planned to use icing sugar because when X-rayed it looks like Semtex. He demonstrated how five packets of icing sugar would be placed in a compartment of the device. "It was one organic substance which could fool even the most sophisticated X-ray machine," he told the court. A piece of iron bar, which could be mistaken for a detonator, was also to have been included.
Mr Hanratty said that the IRA had used a multitude of strategies over the years, including sniper, grenade and mortar attacks, car and lorry bombs and hoaxes. "In Belfast, the IRA have carried out thousands upon thousands of different types of attacks
Mr Hanratty, 38, Martin Murphy, 36, Donald Gannon, 34, Patrick Martin, 35, Robert Morrow, 37, Francis Rafferty, 45, John Crawley, 39, and Clive Brampton, 36, all deny conspiring between January and July last year to cause explosions likely to endanger life or cause serious injury to property.
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