there's no real secret, the theipval memorial is a memorial to the missing on the somme battlefield, it bears the names of the 72,000 men (of the UK and SA) who have no known grave. the battle of the somme which started on the 1st July 1916 and went on until november, just by looking at the date of his death tells you he was killed there
On the 9th Aug 1916, the 1/5th LNLs as part of the 55th Division were attacking Guillemont, starting at 4.20am, they were stopped by the wire and heavy maching gun fire, and suffered severe casualties