The Republic of Ireland's national rail operator, Iarnród Éireann, ordered Mark 3 carriages built between 1980 and 1989, with bogies for the Irish gauge of 1600 mm (5 ft 3 in).
The fleet consisted of 124 Mark 3 and nine Mark 3A Internationals, which worked only the Dublin–Galway service, branded Cú na Mara or Hound of the Seas as it was a coast-to-coast route.

Throughout the 1990s and 2000s they were the backbone of the Irish InterCity rolling stock.

They were built with automatic plug doors, which initially caused some concern as additional time and resources were required to perfect them.
The design was later used on the Class 442 "Wessex Electrics".
Most of the fleet was air-conditioned, except for a small number of coaches built as outer-suburban stock, which ran in push-pull configuration.
A number of coaches were first class, and there were several dining cars and five driving van trailers (DVTs) that included passenger seating.
There were also a number of accompanying generator vans to supply power.

In 2006-07, Irish Mark 4 carriages were introduced on the Dublin-Cork route, with the displaced Mark 3 coaches  to other InterCity routes.

In 2008, Iarnród Éireann began taking delivery of 22000 Class railcars, which led to withdrawal of all Mark 3 coaches.
The type's final service was a Dublin-Cork relief train on 21 September 2009.

Efforts were made to sell the 130 carriages but some were still stored in various locations.
During 2015 some carriages were refurbished for use on the Grand Hibernian luxury train, which began operating on 30 August 2016.

Between 2013 and 2014, most of the Iarnród Éireann Mark 3s were scrapped at Waterford, Dundalk, and Adelaide Depot in Belfast.
The Republic of Ireland's national rail operator, Iarnród Éireann, ordered Mark 3 carriages built between 1980 and 1989, with bogies for the Irish gauge of 1600 mm (5 ft 3 in). The fleet consisted of 124 Mark 3 and nine Mark 3A Internationals, which worked only the Dublin–Galway service, branded Cú na Mara or Hound of the Seas as it was a coast-to-coast route.
Throughout the 1990s and 2000s they were the backbone of the Irish InterCity rolling stock.
They were built with automatic plug doors, which initially caused some concern as additional time and resources were required to perfect them. The design was later used on the Class 442 "Wessex Electrics". Most of the fleet was air-conditioned, except for a small number of coaches built as outer-suburban stock, which ran in push-pull configuration. A number of coaches were first class, and there were several dining cars and five driving van trailers (DVTs) that included passenger seating. There were also a number of accompanying generator vans to supply power.
In 2006-07, Irish Mark 4 carriages were introduced on the Dublin-Cork route, with the displaced Mark 3 coaches  to other InterCity routes.
In 2008, Iarnród Éireann began taking delivery of 22000 Class railcars, which led to withdrawal of all Mark 3 coaches. The type's final service was a Dublin-Cork relief train on 21 September 2009.
Efforts were made to sell the 130 carriages but some were still stored in various locations. During 2015 some carriages were refurbished for use on the Grand Hibernian luxury train, which began operating on 30 August 2016.
Between 2013 and 2014, most of the Iarnród Éireann Mark 3s were scrapped at Waterford, Dundalk, and Adelaide Depot in Belfast.
British Rail Mark 3