I am directing Journey's End by R.C. Sheriff (1928), the first major play written to deal with World War I. Incredibly moving, it is set in a dugout on the trenches of the front line. It was made into a movie in 1930, directed by James Whale and starring Colin Clive, the same combo who later made Frankenstein.
I saw War Horse in London this past summer. I'd like to add my recommendation to Alixz's. The most astounding staging I have seen of anything in years --- you will be in shreds by the end. I was, anyway.