Although I seldom go to the cinema these days I do still buy a fair number of films on (normally cheap second hand) dvds.
'The Trench' (filmed in 1998 i think) depicts the final 36 hours of a group of British soldiers before going 'over the top' in the Battle of the Somme on July 1st 1916.
Apart from the final few minutes,the entire film takes place in the trench and really focuses on the relationships between the soldiers as opposed to the war itself. Its certainly not a gung-ho action packed movie. Its a lot better than that.