For Dame Kiri, it was a deeply moving, poignant experience.
"The story of the Somme is quite horrifying, full of terrible things," the 72-year-old told the Herald.
"But you have to learn about it because it was very real for so many young boys. The experience was something that will stay with me for a long time."
Dame Kiri and Waetford, the 25-year-old who sang with Dame Kiri in a concert on a ship at Anzac Cove for the 100th anniversary of the Gallipoli campaign commemorations last year, spent a week filming on the Somme last year.
While they were focused on finding Kohere's grave, they also stumbled upon Waetford's great, great grandfather's gravesite.
"The young boys who went there on a journey of a lifetime will not be forgotten, and that's just so important," she said.
"Walking through the trenches and fields, and stopping at all of the graves with a silver fern, you feel their spirit.
"The more you go into it, the more devastating it is and the more affected you become by seeing the enormous waste of life."
Joined by expert military historians and scholars, the documentary looks at the Maori story of the Somme, where nearly 6000 New Zealanders were wounded and 2000 died in just two months.
More than half of the Kiwi Somme dead have no known grave.
"I would encourage as many people as possible to visit the Somme," Dame Kiri said.
Sacrifice on the Somme airs exclusively on Maori Television at 8am on Anzac Day, April 25.
