The first was Osprey Elite #6: French Foreign Legion Paratroops the tales of which included Dien Bien Phu, sadly enough. Interesting read.
And then there was Osprey Fortress #24: Fortifications of the Western Front 1914 – 18 which was actually a pretty fascinating look at what both sides did in terms of the trench warfare, and what they built to improve their protection from artillery fire and snipers. Solid read if you have any interest in the history of WWI.