July 21st, 1972, is the other infamous "bloody" day in Northern Ireland's Troubles. It produced some of the Belfast's darkest memories of mutilated corpses strewn across streets and of thousands of people caught in the panic of trying to flee a city centre in which bombs were exploding almost every minute.
Memories of the events remain vividly implanted in the minds of those caught in the horror. But, unlike the British army's killing of 13 people in Derry on Bloody Sunday, the July 21st anniversary has remained largely unmarked.
The lead-up to the IRA's onslaught on the city's commercial heart began some months earlier with the decision by the IRA to call a ceasefire and engage in talks with the Conservative government of Mr Edward Heath.
An IRA delegation travelled to London and held direct talks with Northern Ireland Office ministers in the Chelsea home of Mr Paul Channon, then Minister of State for the North.
The talks failed and by late June the IRA was moving towards restarting its campaign. The breakdown finally occurred because of a dispute over the allocation of houses in the Suffolk area and the IRA and British army became involved in gun battles in Horn Drive.
The decision to step up the IRA campaign centred on an attempt to bring Belfast to its knees. Responsibility for the plan is generally attributed to Seamus Twomey, the uncompromisingly hard-line west Belfast republican, who was probably the IRA's Northern Commander and a member of the Army Council. He died from natural causes some years ago.
The organisation of the July 21st bombings is reputed to have been delegated to his Belfast Brigade Officer Commanding, a man then in his early 20s.
The bombs were strategically placed to bring chaos to the city. As well as the 22 bombs, the IRA telephoned hoax warnings which worsened the panic.
The first bomb exploded at 2.36 p.m. at the Brookvale Hotel, long since closed, in Brookvale Avenue, north Belfast. The area was cleared and no injuries occurred. Bomb warnings were being telephoned every few minutes about devices right across the city.
The second bomb exploded four minutes later at the Ulster Bank on the Limestone Road, only a few hundred yards from the hotel. The area had not been cleared. A local Catholic woman, returning from shopping, was caught in the blast and flung against iron railings, losing both legs. Motorists whose cars were trapped in the traffic were also caught in this blast and injured.
At 2.52 p.m. a bomb exploded at the railway station in Botanic Avenue. Another exploded without warning a minute later on the Queen Elizabeth Bridge, but caused no injuries.
Then seven bombs exploded within four minutes. A car-bomb left outside Protestant houses in Agnes Street exploded at 3.02 p.m. without warning, but caused no injuries. Almost simultaneously a bomb exploded at the Liverpool Bar in Donegall Quay, again without proper warning, but causing few casualties. The next explosion was at 3.04 p.m. in Ormeau Avenue. No warning was given, but there were no injuries. Eastwood's Garage on Donegall Road was then destroyed by a large car-bomb.
A bomb in a suitcase left in York Street railway station exploded as the station was still being cleared, causing some casualties. A landmine was detonated on the road to Nutts Corner, west of Belfast, just as a busload of schoolchildren was passing. The driver saw the device and swerved, avoiding the worst of the blast. The Nutts Corner bombers probably mistook the bus for a British army vehicle.
Another bomb exploded on the bridge over the M2 motorway at Bellevue in north Belfast, but no one was injured. The next explosion was at the footbridge over the Dublin to Belfast railway line at Windsor Park, but again there were no injuries.
At 3.10 p.m. the worst casualties of the day occurred when a bomb exploded outside the Ulsterbus depot in Oxford Street. The area was still busy and the bomb, in a Volkswagen estate car, went unnoticed in the confusion and mayhem which was engulfing the city.
Two soldiers, Cpl Stephen Cooper (19) and Sgt Philip Price (27), who had just alighted from the safety of their armoured car, caught the full force of the blast and were killed instantly. Also killed in the blast beside the bus office were four Ulsterbus employees: Kenneth Crothers, a 15year-old message boy and promising soccer player from east Belfast; William Hill Irvine (18); Thomas Killops (39) and John Gibson (55).
Ten minutes after the Oxford Street explosion a car-bomb exploded outside the row of single-storey shops near the top of the Cavehill Road, a quiet, religiously-mixed residential area of north Belfast. Two women and a man died in this blast.
Mrs Margaret O'Hare (37), a mother of seven children who was married to one of the city's leading Catholic businessmen, Hugh O'Hare, died in her car. Mrs O'Hare had driven across the city from her home in the Malone area to collect her mother when she heard about the bomb explosions in the city. Her 11-year-old daughter was with her in her car and was badly injured.
Miss Brigid Murray (65), a member of a well-known family of Catholic publicans, who had been out shopping, was also killed.
The third victim of the Cavehill Road explosion was Stephen Parker, younger son of the Rev Joseph Parker, chaplain to the Belfast Mission to Seamen. Stephen had been helping to clear people away from the car-bomb when he was caught in the blast. Earlier that day he had told his mother that he felt "something awful" was going to happen.
His father told a reporter later: "If we thought Stephen's death would help bring an end to all this, it would make it easier to bear." Mr Parker later helped to found a cross-community peace movement, but the family eventually left the North to live in Canada.
Five minutes after the Cavehill Road blast a bomb exploded on the railway line near the Lisburn Road, but caused no casualties. Another device, thought to have been abandoned on the Stewarts town Road, exploded at about the same time, causing no injuries.
Other bombs exploded at the Northern Ireland Carriers depot on the Grosvenor Road; in Albert Street; on the Crumlin Road; at Smithfield bus depot and at a seed merchants in Garmoyle Street.
A car-bomb exploded on Salisbury Avenue, causing no injuries and little damage. A bomb on the Sydenham flyover was defused.
Loyalist assassins from the Ulster Defence Association retaliated that night, killing five Catholics, including a young folk singer, Rose McCartney, and her fiance, Patrick O'Neill. They were abducted, beaten and shot dead in a UDA club.
No one was ever charged with any of the murders caused in the bombings, although the individuals responsible for the day's carnage are known.
The IRA described the bombings as an act of war and blamed the deaths and casualties on the security forces for failing to react to warnings. This was rebutted by the RUC, who pointed to the confusion caused by the large number of hoax warnings.
At least one of the IRA figures centrally involved in organising those bombings is closely associated with the moves within the Provisional IRA which have led to the calling of yesterday's IRA ceasefire.