Paul Gross wrote and directed this film, and it's closing song "After the War". Michael Dunne was his grandfather, a WW One vet, who once heartbreakingly confessed to a young Gross about bayoneting the young lad in the forehead. Gross later said on Dunne's deathbed he was muttering for forgiveness and he was the only one who knew what was being talked about.
When filming the Battle of Passchendaele, Paul Gross was very meticulous about maintaining historical accuracy. He would keep various photos of the real battlefield and compare them with how the set looked.
Extras were provided with 5mm wetsuits to make the hours and days of sitting and running in wet and muddy costumes bearable - even still many extras left after one day. A German full length jacket could weigh up to 60Lbs when wet and caked in mud.
When Sarah Mann asks Michael Dunne about the Battle of Vimy Ridge (where her father died), Michael answers that we "was in that fight". Actor Paul Gross (Michael Dunne) actually narrated the documentary "The Battle of Vimy Ridge - Part 4: The Battle Joined and Won" in 1997, ten years before the production of "Passchendaele".
The scene at the beginning of the battle of Passchendaele where Canadian soldiers walk on wooden planks between the wet trenches is virtually identical to a famous picture of the battlefield taken by Australian photographer Frank Hurley on October 29th 1917.
A group of extras (Military members among them) camped near the Tsuu T'Ina battlefield set in what became known as "Camp Hornburg", named for Corporal Nathan Hornburg who was killed in Afghanistan, September 24th, 2007 - close to the filming dates.