The following is a write up of some info I put on the boards.ie WW1 forum re looking for information about Irish soldiers in the British Army in WW1. This is an evolving entry.
Soldiers who died or were killed
A soldier who died during the period 1914-1921 should have an entry in the Commonwealth War Graves Commission (CWGC) database, an entry in Soldiers Died in the Great War (SDGW), Ireland's Memorial Records (IMR) if an Irish soldier (or in an Irish Regiment or of Irish parents), or De Ruvigny's database/book.
Some soldiers have been omitted from the CWGC list and there is a project to bring these soldiers In From the Cold.
A soldier should also have a medal index card (MIC) if he served in a theatre of war. A Medal Index Card outlines the medals a soldier was awarded. The UK National Archives website has a good explaination of the Medal Index Cards and the WW1 Campaign Medals and awards.
A soldier should have a service record but most of these were destroyed in the bombing of London in World War 2.
A new online resource is the wills of approximately 9000 Irish soldiers. These are free to view. The UK Government has a similar site for WW1 soldiers wills but charges for access should you find a match for the soldier you are seeking.
Some Irish soldiers may have signed the Ulster Covenant and you may find a copy of their signature on the Ulster Covenant database.
You may find an entry on Irish War Memorials website or www.Findagrave.com.
A soldier who didn't serve in a theatre of war but was killed during the Easter Rising, for example, or died from disease or as a result of an accident in England/Scotland/Wales/Ireland won't have a medal index card (MIC) but should have an entry on CWGC.
In general, there is more data available about a soldier who died than there is about a soldier who survived.
Members of the Irish Association of Volunteer Training Corps
Members of the Irish Association of Volunteer Training Corps (IAVTC) who were killed during the Easter Rising do appear in Ireland Memorial Records (IMR) but because they were not members of the armed forces, they do not appear in SDGW nor do they have an entry on the CWGC database or a CWGC grave. They do not have a medal index card. The IAVTC men killed were not British Army reservists nor were they members of the Ulster Volunteer Force affiliated Loyal Dublin Volunteers.
Soldiers wounded and discharged
A soldier wounded and discharged should have a medal index card (MIC), may have a service record, possibly a Silver War Badge (SWB) entry and possibly a pension record.
Soldiers who served in a War Theatre and Survived
A soldier who served in a theatre of war and survived should have a medal index card (MIC) and may have a service record.
Soldiers who didn't serve in a War Theatre and Survived
A soldier who didn't serve overseas and survived may have a service record but won't have a medal index card (MIC).
The service records of soldiers who served in the Irish Guards are still held by the regiment and can be obtained by writing to them at :
RHQ Irish Guards
Other Guards regiments (Scots. Welsh, Grenadier, Coldstream) also have their records stored and available at the above address - just change the regiment name after RHQ.
Other Family Members in the Armed Forces
In some instances, if the soldier had a brother who served, you may find the brother has a service or pension record that mentions the man you're looking for.
Each battalion was required to keep a war diary but ordinary soldiers rarely get a mention by name.
Soldiers awarded medals for bravery can be found in the London Gazette database. This can be a challenge to use at times.
Other sources can be a bit hit and miss. Local newspapers carry some info about enlistment, being sent to the front, being wounded, on home leave or killed/missing/taken prisoner.
Rolls of Honour
Some employers, schools and colleges have produced lists of people who served as well as those who died e.g Guinness, Trinity College, Bank of Ireland. In some cases, researchers such as Tom Burnell have produced books (Wexford War Dead, Waterford War Dead, Carlow War Dead etc) which have gathered together CWGC, SDGW, IMR and newspaper data. The Dublin City archive at Pearse Street has a roll of honour for those from Dublin who died. There is a also an officers roll of honour at Pearse Street.
Moving between battalions and regiments
It's not uncommon to find soldiers moving between battalions within a regiment or from one regiment to another. In some instances this would involve moving from a training battalion to a front line battalion within the same regiment or to another regiment if it had suffered large casualties.
Later in the war, some battalions who suffered casualties were disbanded and their remaining men were sent to other battalions/regiments. In some instances men were compulsorily transferred to meet the needs of the army e.g. cavalrymen weren't needed and could be transferred en masse or it might be that a man had a civilian skill that might be better used elsewhere e.g. a driver to the Army Service Corps, a miner to a Tunnelling Company etc. Without the service record for your man it would be hard to say why he has moved between regiments.
A soldier's number was issued by his regiment (or battalion). If he moved to another regiment he would be issued a new number.
Bureau of Military History Witness Statements
A number of soldiers completed Witness Statements (WS) for the Irish Bureau of Military History (BMH) or are mentioned by members of the old IRA. Always worth a search but it would be a long shot.
Sources of Advice
Great War Forum
Boards.ie WW1 sub forum
Dublin Western Front Association
My Soldiers and Sailors
Sapper John Shepley from Wheelock, Royal Engineers (died 1943 of wounds received Nov 1918)
Private James Shepley from Wheelock, Grenadier Guards (DoW 1915)
Private Joseph Clarke from Macclesfield, 15th Battalion Cheshire Regiment (Bantams) (KIA October 1918)
Private James Wildblood, 6th Battalion Royal Fusiliers (Died 1917)
Lance Corporal Roy Cooke from Sandbach, Grenadier Guards (KIA Italy 1944).
Chief Gunner John David Sumner, HMTB 96, died 1st November 1915. From Portaferry, Co Down.
Sapper Joseph Niland from Dublin, 179th Tunnelling Company, Royal Engineers (KIA March 1917).
Private George Sweeney from Dublin, Royal Munster Fusiliers (KIA 1917).
Michael (Mickey) Sweeney from Dublin, 4th ASU Dublin Brigade, fought in the Easter Rising and Irish War of Independence; killed April 1922.
William Patrick O'Brien, Queenstown Company, Irish Volunteers, died November 1916 after release from Frongoch (Sigerson Cup winner with UCC 1911)
KIA = Killed in Action
DoW = Died of Wounds
Also fought/served :
Fred Shepley, Wheelock, Royal Flying Corps
Harold Shepley, Wheelock, Cheshire Regiment
Grace Shepley, Sandbach, Volunteer Aid Detachment, Egypt
John Newton, Wheelock, Cheshire Regiment
James Alexander McCullen, Portaferry, Merchant Marine
Charles Skilbeck Smith, Salop, RNAS
Richard Skilbeck Smith MC, Salop, Middlesex Regiment and Indian Army
Abram Jones, St Asaph, Welsh Guards
Thomas Williams, St Asaph, Royal Engineers
Irish War of Independence
John Joe O'Brien, Irish Volunteers, Galbally Company, IRB, IRA, Free State Army
Ned O'Brien, Irish Volunteers, Galbally Company, IRB, IRA, Free State Army
Josef Ciupak, Free Polish
Cyril Humphrey, Crewe, Royal Air Force
John Doyle, Enniscorthy. Free State Army, 1930s
Daniel Doyle, Dublin, Royal Air Force 1950-1979
xxx xxxxxx, Dublin, Special Air Service
Ben Oliver, Macclesfield, Royal Marines