The bomb, which was built into a converted lorry, went off as thousands of people were leaving work and going home, John Bevan QC told Woolwich Crown Court in east London.
James McCardle, 29, a labourer from Crossmaglen, Co Armagh, denies conspiring "with other persons unknown" to cause an explosion likely to endanger life or cause serious injury to property between 30 October 1995 and 10 February 1996.
He also denies murdering Inam Bashir and John Jeffries, the two who died in the blast.
Mr Bevan said the explosion, at South Quay at 6.59pm on Friday 9 February 1996, was "enormous" and brought to an end the first 18-month ceasefire by the IRA.
He went on: "Inaccurate and, from the point of view of timing, wholly inadequate warnings were given by telephone from a number of people. These warnings did not begin to give police sufficient time to warn and evacuate the many thousands of people working and leaving work in the area."
A policeman managed to warn Mr Bashir and Mr Jeffries to leave but they "did not act immediately... within a few minutes they were killed instantly when it went off."
Mr Bevan told the jury that a "meticulous investigation" had traced the bomb lorry's history to Northern Ireland. A month before the blast, it had been taken on a practice run to Carlisle.
"It was a major IRA operation which must have involved a large number of people, each with their own explicit role in the planning of it, the conversion of the lorry and the housing, the storing of the lorry and, of course, the manufacturer of the bomb inside the lorry."
He said McCardle's alleged role was a "central one at the forefront of the plan".
His finger, thumb and palm prints were found on a number of items which could be linked to the practice and bombing runs.
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