Troops in training jumping over a trench, 1916 (c)

Photograph, World War One, Western Front, (1914-1918), 1916 (c).

Trenches were not dug randomly, but were part of a complex design. Each of the front line trenches was backed-up by second and third lines: 'support' and 'reserve' trenches. Communication trenches linked them all together. The support and reserve trenches were lined with underground shelters or dug-outs which were used as protection from enemy fire and the weather.