Bill asked:
I would like to hear David's and others opinions on how essential safe havens were for the IRA.
I shall limit my remarks to 'The Troubles' 1969-1998, although clearly history, tradition and culture had an impact.

The Republic of Ireland (Eire) was always a potential safe haven and the various Irish Republican groups, primarily the Provisional IRA (PIRA), were careful to stay away from challenging the Irish state. The border was never truly "sealed", although curiously it was during a mainland Foot & Mouth epidemic in 2001 and Irish action was very thorough - with a heavy civil & military presence for part of one year (Eire was very dependent on agriculture then).

PIRA certainly by the 1990's relied on "safe havens" in a few areas, usually lightly populated such as Co. Donegal or where local support (passive & active) and extensive cross-border links existed - opposite 'Bandit Country' (See Toby Harnden's book 'Bandit Country:The IRA & South Armagh', pub. 1999) or Co. Armagh & Co. Fermangh. This enabled either safe training and preparation of IEDs, although not to the extent of being undisturbed. At one time attacks across the border were common, from sniping to IED ambushes, e.g. Warrenpoint in August 1979:http://en.wikipedia.org/wiki/Warrenpoint_ambush

The Irish state did - after a few years - consider PIRA and other groups as threats to the state, responding with searches, intercepting arms smuggling (notably from Libya), handling informants and arrests. It didn't help that bank raid or cash in transit attacks, IIRC the main source of funds, one day led to an unarmed Gardai officer being shot dead - which IIRC led to a massive adverse public reaction. Eventually suspects were extradited across the border and to the mainland. For example:http://en.wikipedia.org/wiki/Dominic_McGlinchey

What is often overlooked is that PIRA activity across Northern Ireland gradually shrank. Londonderry had a long standing, informal ceasefire in the city and rare, if bloody cross-border attacks. West Belfast took far longer to scale down or reduce. Towards the end the focus was in the cross-border 'Bandit Country', notably the elusive and deadly sniping attacks (using imported US Barrett rifles).

Also PIRA's character changed over the years. The number of Ulster born / resident participants in the violent campaign dwindled and were replaced by the more "hard core" Republican communities, many who had lived further & further away from Ulster itself. (See Kevin Toolis book 'Rebel Hearts:Journeys within the IRA's soul', pub.1995)

Essential? Certainly not at the beginning, when the focus was in the urban areas mainly and PIRA had extensive public support. As the struggle evolved use of the Irish Republic became essential, if sometimes dangerous and at the end PIRA's violent campaign depended on using certain "safe havens".

The Irish state and the Irish public after the mid-1980's made it quite clear the Republican struggle was not for them. It took time for this to be reflected in co-operation between the law enforcement bodies - the two police forces became very close (not co-operation with the British military) and in political engagement to achieve cross-community agreement.