There are 2 DVD sets that are well worth getting
'The Great War' - a series done in the 1960s about WWI and has not been bettered. It interviews blokes who survived the trenches. Pretty horrific, but shows it for what it was.
'The World at War' - about WWII; the series from the early '70's. Again, it's so hard to improve on such a thorough and in-depth box set. Some of the footage should be mandatory in school lessons.
I did my degree in Modern History, but these days, I have trouble getting through old footage like that without weeping.
I remember seeing a programme about a French Farmer ploughing his field and uncovering a hole where some steps led downwards. They got a few experts to excavate it - it turned out to be part of a British underground explosive mine laying network. They'd tunnel under the German trenches and pack it with TNT. Then detonate it. The Germans were doing exactly the same to the Allies btw.....
Like this;
http://www.youtube.com/watch?v=YPGrrnpzB_Y
The immediate area was still in good nick - down below, they discovered bullets embedded in the wooden props holding the roof up. They came to the conclusion that the German tunnel crews had broken into the British tunnels and an underground battle had taken place - though it was a fairly common event. Tunnels were often dug deliberately to catch the opposition out before they could detonate explosives - the British Army recruited many tunnel diggers from the then-new London Underground rail system (aka 'claykickers')