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It is likely that some of the men who feature in the photos perished in the bloodbath during the Battle of the Somme later that year.
Remarkable never before seen photos of British Tommies on the frontline have come to light over 100 years later.
They were collected by German infantryman Walther Hader who fought against them on the Western Front in World War One.
His unusual hobby was to pick up images of his adversaries he found in shell craters, seized trenches and abandoned buildings.
Hader was called up aged 19 in August 1917 and took part in the 1918 German spring offensive before his capture that May.
He spent the rest of the conflict in Leigh POW camp in Greater Manchester before being repatriated in 1919.
German historian Rob Schaefer, who has come into possession of the photos, is trying to identify the 'lost faces' so he can tell their stories.