Hi Stephen
I found the following records for Thomas William Archer Mullen born 1896 in Birmingham (parish of Aston, Warwickshire):
On 7 Aug 1914 (age 18) he enlisted in the Royal Tank Corps at Stratford (Tank corps number 7816449, Service number 7816449). At that time he was a casual laborer.
DUBLIN CONNECTION
By 1916 he was stationed in Dublin at Marlboro Barracks (now McKee Barracks) near Phoenix Park in Cabra.
On 1 June 1916, he married Christine Flood (age 17) in Dublin's Pro-Cathedral on Marlborough Street.
Christine (aka Chrisdina aka Dina) Flood was born and raised at Anglesea Market, Coles Lane, Dublin (near Moore Street). Her older sister Kathleen Flood witnessed the marriage.
From the 1911 Census, we find her parents, Michael & Margaret Flood (married 13 years, with 5 children) residing at 1 Anglesea Market (over a shop). Michael Flood was a printer and the family occupied 3 rooms on this premises. Previously, at the time of the 1901 Census, he was a laborer.
Thomas William Archer Mullen's father, Thomas Mullen Sr., was recorded as a clerk.
Between 1917 and 1923, they had 3 children (Thomas Michael Mullen, Michael Patrick Mullen, and Elizabeth Mary Mullen) all born in Dublin according to his enlistment records.
Your Great Uncle served in France during WWI (from Nov 1916- Jun 1918) and was discharged on 8 June 1926, at which time his address was 1 Anglesea Market Coles Lane, Dublin.
This means you should definitely add them to the Ancestors' Roll-Call for St Marys Dublin and attach Thomas to Military ancestors for Grangegorman as well.
AUGHRIM CONNECTION
If the Aughrim baptism is indeed his, it looks like he got baptised (a week before his wedding) in order to marry this Catholic girl. But why go all the way Aughrim, Co Roscommon?
What other details are on this record? Would you be able to attach an image of it?
I suspect that the baptism record may actually be for Aughrim Street Church (which is in Cabra, Dublin 7 near his barracks).
Hope this helps!