The trenches were very cramped and dirty. They were incredibly infested with rats and possibly many other unknown organisms. They had many advantages and disadvantages. The advantages were that it provided cover for the men against many bullets and grenades however it put the men in a certain position where there backs were against the walls and it took away mobility. Basically if one grenade landed in a trench it could kill up to 5 men. Also disease spread quickly through the trenches. It only took one man to catch an infectious disease and the entire platoon could be infected in a matter of days.