The Bring Them Home project is the latest event being staged by the Royal Welsh Fusiliers Museum to illustrate the extent of the losses suffered by just one regiment in the 1914-18 conflict.
One RWF soldier killed in action on a Flanders battlefield in 1917 was poet Hedd Wyn.
As well as displaying the names of the Fallen on the walls of the castle, which houses the regimental museum, the organisers hope the event will spur families to send in photographs of family members who died in the war.
Shirley Williams, Museum Development Manager said: “The names of those who fell are marked on war memorials in towns and villages across Wales, but we think this event will help to bring the boys together to show the horror inflicted on just one regiment.
“It’s particularly poignant because we will shortly be marking some of the big battles of the war - like Mametz Wood and the Somme where large numbers from the RWF lost their lives.
“We are also hoping this project will add to the collection of photographs we’ve been compiling of the soldiers who died, which we are displaying at the Museum on the centenary of each man’s death. Currently, we have gathered around one in eight of those who never came home.
“We would dearly love to bring all the boys back together again in pictures if at all possible - and perhaps project their faces on the walls of Caernarfon Castle in 2018 to mark the end of the War”.
Relatives with photographs are being asked to bring to the RWF Museum, Caernarfon Castle or email to email@example.com where they can be scanned and kept safe for posterity.
The screening has been made possible by HLF funding. Richard Bellamy, Head of the HLF in Wales said, “The centenary of the First World War is an important opportunity for us all to pause and reflect on the sacrifice of all those involved in conflict.
“War memorials remind us of that incredible sacrifice and I am really pleased that National Lottery money is being used to help people to find out more about the people and stories that they represent, in a new and different way.”
Pupils from Ysgol Bontnewydd will be attending the museum on Sunday morning, dressing up in WW1 costume and going over to the War Memorial in Castle Square for 11am.
The Last Post will be played from a castle tower at 11am.