A search for the Brennan family name gave me 462 results.
343 who served with the United Kingdom Forces
64 with the Australian Forces
12 with the New Zealand Forces
40 with the Canadian Forces
3 with the South African Forces
6 of the records are for soldiers commemorated in Ireland
Francis A Brennan Service Number 25244 of the Royal Dublin Fusiliers died 1916
John Brennan Service Number 9952 of the Royal Irish Regiment died 1916
John Brennan Service Number 27864 of the Royal Welsh Fusiliers died 1918
John Brennan Service Number 24999 of the Royal Dublin Fusiliers died 1918
Moses Brennan Seaman of the Merchant Navy died 1940
Thomas Joseph Brennan Service Number 1835395 of the Royal Artillery died 1941
Moses Brennan is such an unusual name that I couldn't help but do a quick search to see if I could find him.
I found a Moses Brennan, son of Edward Brennan and Kate Roche born on March 7th, 1898 at Trimmer's Lane, Wexford. In the 1901 Census Moses aged 3 was living with his parents Edward & Catherine and siblings, Patrick, Edward (Moses twin), and Katie. Moses uncle John is recorded as a sailor. By 1911, Moss mother is recorded as having birthed 10 children of whom only 5 are living.
In 1922, Moses, occupation Sailor, married Alice Doran of Scholar Street., Wexford.
Commonwealth War Graves Commisssion
Birth Cert 1898
1901 Census Wexford
1911 Census Wexford