The Allies used four "types" of trenches. The first, the frontline
trench (or firing-and-attack trench), was located from 50
yards to 1 mile from the German's front trench. Several
hundred yards behind the front-line trench was the support
trench, with men and supplies that could immediately assist
those on the front line. The reserve trench was dug several
hundred yards further back and contained men and supplies
that were available in emergencies should the first trenches be
overrun. Connecting these trenches were communication
trenches, which allowed movement of messages, supplies, and
men among the trenches. Some underground networks
connected gun emplacements and bunkers with the
communication trenches.