« Reply #71 on: Sunday 11 September 11 14:33 BST (UK) »
It doesn't look like a funeral of a clergyman. Archbishop Walsh was brought from the Pro-Cathedral to Glasnevin - a long way from Dun Laoghaire.
I think the possibility that shanghaipanda suggested is a very strong one:
John Jenkins
On the 4th of May 1921 a Volunteer with the Dun Laoghaire I.R.A. stationed at the naval base in Dun Laoghaire died as a result of an accident. Volunteer John Jenkins was cleaning his rifle when he accidentally discharged it resulting in a fatal bullet wound to the head. John Jenkins had served ten years in the British Army before returning to Ireland and joining the I.R.A.
John Jenkins lived at Saint Mary’s Cottages Monkstown and left a wife and six children. He was given a funeral with full military honours and many National newspapers reported on the large procession that followed the coffin as it was taken to Dean’s Grange Cemetery. The Procession included comrades from the Naval Base at Dun Laoghaire as well as other I.R.A. units as well as Fianna Scouts, ex-service men and a fife and drum band. John Jenkins was laid to rest in the Republican Plot.
The gentleman in the London bobby style helmet looks like a pre-Garda Síochána officer, which would put it pre 1925 I believe.
It would make sense for the funeral to be taking that route if they intended to walk (as is common in Irish funerals) past his home in Monkstown on the way to the cemetery at Deansgrange.
Coffey, Cummins [Rathfalla, Tipperary], Cummins [Skirke, Laois], Curran, Dillon [Clare], Fogarty [Garran, Laois/Tipp], Hughes, Keshan (Keeshan), Loughman [Harristown and Killadooley, Laois], Mallon [Armagh], Malone, Markham [Caherkine, Clare], McKeon(e) [Sligo/Kilkenny/Waterford], McNamara, Meagher, Prescott [Kilkenny/Waterford/Wexford?], Rafferty, Ryan, Sullivan, Tobin
GEDMatch: T665306 tested with Family Tree DNA and also with ancestry
GEDCOM file: 1980344