Commenting on the protest by supporters of the H-block hunger strikers on July 18th, 1981, in Ireland 1912-1985, the historian, J.J. Lee, praised the then minister for justice Jim Mitchell for "a striking sureness of touch in handling an ugly situation".

It was correct to acknowledge civilian control of the police service in a democratic society. But Joe Lee's economy of words passed over the contribution of the command-and-line garda∅ who manned an bhearna bhaoil - a crucial turning-point in modern Irish history.

In anticipation of the march, planned to end in a demonstration at the British Embassy, the government made the strategic decision to halt the protesters short of their objective, to avoid the mayhem that occurred in Merrion Square on February 2nd, 1972, when the embassy was burnt by an angry crowd protesting against the Bloody Sunday shootings in Derry.

One of the most experienced senior Garda officers in the city, Chief Supt John Robinson, of C-District, Store Street, was directed to take charge of tactical operations. Recently promoted, "Robbo" was respected as a charismatic leader by rank-and-file garda∅.

In the forenoon of Saturday, having surveyed the approaches to the embassy, he closed off Merrion Road at the Simmonscourt Road junction, using standard interlinked metal fencing strengthened by chains anchored at either end to the RDS railings and the stout base of a lamp standard; but the barrier was to collapse under the unexpected ferocity of the rioters.

Chief Supt Robinson took command of a force of 500 garda∅, drawn from city stations and reinforced by contingents from the provinces, who had little or no experience of confrontation with unruly assemblies and were unprepared for what lay ahead.

Compared with the body-length armour and head-to-foot protective clothing now available, the hand-held plastic shields and cork helmets provided for riot control were inadequate; and there were not enough shields to go around.

Word arrived that trouble-makers among the marchers had damaged business premises in the city and attacked with stones and banner poles a detachment of garda∅ on duty at Leinster House.

Addressing his men assembled in the Royal Dublin Society showground, Chief Supt Robinson appealed to their patriotism. Their country and the reputation of the force depended on them; the eyes of the world would be watching. Having detailed a reserve of 150, and a smaller number at the British Embassy, where an Army contingent was standing by, he stationed his main force at the barricade: about 300 garda∅ to stop an awesome crowd of 15,000 advancing from Northumberland Road.

As the marchers came into sight at 4 p.m., the tall, heavily built commander moved through the ranks of helmeted garda∅, exhorting them in the event of trouble to stand fast in their good discipline. Frontline command positions on either flank were taken up by Supt Tom Brennan, of Pearse Street, and Supt John F. Hughes, of Kevin Street. A deputation was admitted behind the lines to confer with Chief Supt Robinson, who told them that under no circumstances would the demonstration be allowed further down the street.

As the deputation rejoined the crowd, missiles rained down; "the air was thick" with stones, bricks and bottles. Garden walls and railings were demolished for ammunition. Some petrol bombs were thrown, and cars, vans and a lorry were overturned and burned. A loud-hailer was used to urge the crowd to push forward, and a cry was heard: "Burn the Embassy!"

For half an hour, Chief Supt Robinson's splendid garda∅, poorly equipped, stood their ground against anarchy, accepting everything the rioters could throw at them. As injured garda∅ were withdrawn from the front line, they were replaced by men from the reserve force. In a classic battle strategy, the rioters targeted the Garda commander himself, who sustained multiple injuries, including a serious leg wound, from which he was not to recover.

The incomparable Chief Supt John Robinson, in great pain and supported on his feet by one of his inspectors, gave the order to draw batons. To negotiate the upturned fencing, the men had to drop their guard; in the heat of battle failing at the first attempt to scramble over the tangled metal.

Characteristically, Chief Supt Robinson was reluctant, as he saw it, to abandon his men at the moment of greatest danger. At the insistence of his lieutenants, Supt Brennan and Supt Hughes, he was carried off the battlefield and taken to hospital. Immediately afterwards, Brennan himself was among the injured removed to hospital.

In the attack on the cordon and during the baton charge afterwards, 200 were injured, including 120 garda∅. These were the known casualties, treated in six city hospitals. Innocent bystanders, who should have left the area as the riot reached its crescendo, were inevitably overrun in the baton charge.

The next morning, Det Supt Pat Doocey escorted the then taoiseach, Dr Garret FitzGerald, on an inspection of the debris-strewn battlefield. Dublin Corporation had to remove tons of rubble from the scene.

In a strong editorial, The Irish Times condemned "the onslaught on the garda∅ . . . clearly planned and organised in advance . . . Questions will be asked about the role of the garda∅. There will be allegations of over-reaction . . . but the garda∅ did their duty, which was to protect the Embassy; and discharging that necessary duty they suffered severe casualties. They must have public support . . . "

Twenty years ago, the thin blue line stopped anarchy in its tracks. The Ballsbridge riot was a watershed in modern Irish history. Providentially, it was not necessary to order the Army reserve force into action. If the embassy had been sacked a second time, the reputation of the State would have been gravely damaged internationally. It would have taken the nation a generation to recover from the psychological wounds.

The H-block hunger strikes began on October 7th, 1980, and were called off on December 18th; re-commenced, they ended on October 3rd, 1981. Ten prisoners died.

Gregory Allen is author of An Garda S∅ochβna - Policing Independent Ireland 1922-1982, published by Gill & Macmillan