Saw this over on the OFF forums. Yeah, its TV archaeology, but its still pretty interesting...and they did actually find parts of it.
http://www.telegraph.co.uk/news/newstopics/howaboutthat/7697251/Secret-terror-weapon-of-the-Somme-battle-discovered.html
http://en.wikipedia.org/wiki/Livens_Large_Gallery_Flame_Projector