Mr Cahill's IRA career almost ended in 1942 when he was sentenced to death for the murder of a policeman. Reprieved, he was arrested 30 years later on board a ship bringing arms from Libya to Ireland and jailed.
He was welcomed yesterday with the same affectionate reverence as Labour Party conferences accord those elderly socialists who knew Keir Hardie. And Sinn Fein has one thing in common with Labour these days: it is still hopeful of ultimate victory, but aware that it is some distance away.
In Labour the talk is of change while in Sinn Fein there is much more emphasis on continuity. It believes the solution to the Irish problem is British withdrawal, and that this can only be accomplished by force. Yet there has also been some intriguing language from the party which hints at some fresh thinking among its leaders.
Speeches and statements have mentioned the need for a period of peace before British withdrawal, indicated that party thinking is evolving, and paid some attention to the question of the rights of others with different opinions, such as Protestants and constitutional nationalists.
Such comments have brought cautious welcomes from Protestant and Catholic clergymen and indeed, most unusually, from the Ulster Volunteer Force. The UVF welcomed the 'departure from republican dogma' and said Sinn Fein had entered the real world.
Sinn Fein denied that the comments represented any significant shift, but it is fairly clear they were designed to catch the attention of the authorities and other sections of opinion, and create speculation on the value of opening a dialogue with Sinn Fein.
Senior Protestant and Catholic clergymen, and probably others, have been in contact with the party, spurred mainly by the hope that the IRA might be persuaded to give up its campaign of violence. But all the public signs are that the British Government sees no value in opening contacts, probably believing there is no point and that such moves would break up the talks that involve Dublin and the four main constitutional parties. Certainly, the RUC and Army show no sign of believing that the republicans are contemplating any ceasefire.
There are, for the IRA, reasons for and against ending the violence, but there is no sign that any 'doves' have ever come close to persuading any 'hawks' that the time has come to stop. In any event, the formidable armoury at the IRA's disposal in itself represents the clincher; with such large amounts of hardware, ceasefire becomes virtually unthinkable.
This year has not been a good one for Sinn Fein, which received a body blow with the loss of Gerry Adams's Westminster seat. Militarily, however, it has hit Belfast hard with destructive car-bombings, as well as continuing its campaign in Britain.
The hope for many is that some in the ranks will at some stage conclude that the violence has not worked, and will not work. But it is also a fact that for many republicans the campaign has become an article of faith, that the use of force has ceased to be a tactic and been elevated to a principle, and that to many the IRA is a killing machine with no off switch.