There’s a fascinating article on my favorite World War I site about J.R.R. Tolkien’s experiences with the horrors of the Western Front. According to his daughter, he actually modelled Frodo, Sam and Gollum’s journey through the Dead Marshes in on the bombed out and devastated battlefields of Belgium and France.
the Journey through the Dead Marshes (in The Two Towers), looks very much like a description of the marshy and swampy battlefields in Northern France and in Flanders. In the course of the war these areas were transformed into deadly mud swamps with slithery clay and shell craters filled with water and corpses. Innumerable soldiers lost their footing and drowned in those treacherous pits.