Before going to the Somme, the soldiers of the 36th Ulster Division trained at Clandeboye Estate, near Bangor, in 1914-1915.
It was a cold, wet autumn and winter and the grounds were awash with mud. That made the estate a perfect training ground for the battle that lay ahead of the men.
Among them was Captain James Samuel Davidson, the heir to the Sirocco Works in Belfast. Jim, as he was known, had a sense that he and his men were an important part of history.
So he began to take photographs. The pictures lay hidden for years.
"It was his great-great nephew who discovered the glass negatives," said Heather McGuicken, the manager of North Down Museum.
"It was such an amazing collection. The images had never been seen before, they had just been glass negatives sitting in a wardrobe for years and years until the family discovered them again.
"They realised what an important historical artefact that they had, what an important collection that they had."
The collection was digitised and donated to the North Down Museum.
The pictures detail the day-to-day life of the training camp.
They show the men practising digging trenches, training with guns and doing their military drills.
Many of the faces are smiling and happy, despite the conditions and the war they were preparing for.
"Jim recognised that very early on," said Heather.
"So we have lovely images not just of 36th Ulster Division training in Clandeboye, but also of the Ulster Volunteer Force. I think he realised it was an important time in history."
Apart from the scenes at Clandeboye, the photos also show the men making the move to England to continue training there.
Jim's engineering background made him a valuable asset to the Army. Hardworking, wealthy and intelligent, he trained with the machine gun corps and quickly rose through the ranks to become a captain.
He went into battle on the first day of the Somme.
"I think Jim Davidson was a man born into wealth," said Heather.
"But I don't think that wealth really meant much to him. I get the impression his family very much had a community spirit, a patriotic spirit.
They were there to serve their country and I think they did that very well. I think Jim answered the call."
That call brought Jim and 19,000 other young men to their deaths on 1 July, 1916.
He left behind a fiancée, a family and a historical record of times before the reality of war hit.