The trouble began in July 1969 as a result of the breaking-up of a civil rights march in Londonderry in which the Protestant paramilitary police (B-Specials) used considerable violence against the largely Catholic protesters.

As the violence spread and Catholics across the province found themselves under attack by groups of Protestants, the decision was taken to reinforce the Northern Ireland garrison with additional soldiers acting "in aid of the civil power".

Initially they were made welcome, especially by the Catholic community. But the good relations did not last, particularly after the rump of the Irish Republican Army entered the fray to continue the fight as the Provisional IRA (PIRA).

As Patrick Brogan put it in his study World Conflicts, a vicious cycle of terrorism and repression was soon under way in the province: "In the aftermath of the Londonderry disturbance in August 1969, Catholics set up no-go' areas in the Catholic districts of that city (the Bogside) and of Belfast (around the Falls Road), building barricades and preventing the police and army from entering. The IRA developed rapidly behind those barricades."

For the British Army, Northern Ireland was soon to become familiar territory as its regiments began the long cycle of six-month roulement tours, or longer accompanied deployments of up to two years. The 1st Battalion The Black Watch was deployed in the province for two short tours in 1970, followed by a longer tour of duty in the "bandit country" of South Armagh and another tour of Belfast towards the end of 1971.

All told, the Black Watch completed 11 tours of Northern Ireland before a ceasefire brought the fighting to a close in the 1990s.

Each tour brought its own challenges in helping to keep the peace and maintain a sense of proportion in one of the most difficult and long-lasting counter-insurgency wars fought by the British Army. Even when peace of a kind was restored in the 1990s, the bad feeling did not disappear.

Some idea of the continuing bitterness caused by the Troubles in Northern Ireland can be found in attitudes which are still prevalent among the Irish community in the US.

Since 1959, the pipes and drums of the Black Watch have made regular tours of North America and in 1963 were invited by President John F Kennedy to play on the South Lawn of the White House. Nine days after their appearance on November 13, Kennedy had been assassinated, and at the request of his widow Jacqueline the pipe major and eight pipers of the regiment led the funeral cortege to Washington Cathedral.

However, in 1971, two years after the Troubles had broken out in Northern Ireland, the pipes and drums of the Black Watch were heckled by crowds during a goodwill tour of the US.

Even in January 2006, a decade after the official ceasefire in the province, the re-appearance of The Black Watch pipes and drums in the company of the band of the Welsh Guards was still enough to encourage the Boston Cumann council of the Irish Freedom Committee to mount pickets and issue a statement of condemnation linking incidents in the province with the regiment's service during the War of Independence: "The record of the Black Watch in Ireland is one of bloody enforcement of British military rule the history of the Black Watch includes decoration for combat against American citizens during the Revolution for United States Independence."

It seemed a poor reward for over a quarter of a century of service in the province where young soldiers of the Black Watch not only had to struggle to keep the peace, but also put their own lives in the balance while carrying out their duties.

As an article in regimental magazine The Red Hackle explained in 1976, the bottom line of the British security operation in Northern Ireland was provided by young soldiers who carried an enormous burden of responsibility upon their shoulders.

"He is ordered into the streets of Belfast with a weapon in his hands, live rounds in his pouches, enormous powers at his disposal, and then told that he is dealing with normal British subjects. He has been trained as a soldier, how to observe, how to seek out a target and how to shoot. Suddenly he is thrown into a situation where he has to make the terrible decision between being polite and firm at one moment and shooting to kill in self-defence at another.

"He is put through tremendous demands in his personal endurance, resulting from the long hours and the peculiar strains and pressures of his position. At the same time he must show almost superhuman patience and self-restraint when patrolling and attempting to help a community that to him appears only to be antagonised by his presence."

With good reason, a wry comment was made at the time that a mistake made by a lance-corporal on the streets of Belfast could plunge Northern Ireland into chaos or bring down the government in London. It was often as serious as that.

Extract from The Black Watch: A Concise History by Trevor Royle, Mainstream, £12.99