The trench system during World War One consisted of at least three parallel trench lines dug in zig-zag patterns. The zig-zag pattern prevented enemy combatants from firing directly down the line of trenches. Parallel trench lines were interconnected by perpendicular communications trenches.
The front-line trench or outpost line was usually situated closest to No Man's Land. In war, No Man's Land constitutes the area between opposing trench systems. During World War One, most front-line trenches were protected by sand-bag walls and barricades of tangled, barbed wire. Front-line trenches were usually only about eight feet deep, but by 1918, the Germans had managed to construct trench systems that were at least 14 miles deep in some areas. Bolt-holes were often carved out on each side of the front-line trench to allow soldiers to eat, rest, or sleep. The front-line trench was most vulnerable to attacks and reported the greatest number of casualties during battle.
Behind the front-line trench was the support trench, situated some 75 meters behind the first trench. The support trench often contained first-aid stations and makeshift kitchens to serve the needs of soldiers on the front lines. Support trenches also housed extra reinforcement forces to replace fallen soldiers from the front lines.
The reserve trench was situated at least 300 meters behind the support trench. Reserve trenches were rarely overrun; because of this, they housed newer soldier recruits, extra medical supplies, food, and cook personnel.
The communications trenches ran perpendicular to the front-line, support, and reserve trenches. Communications trenches facilitated the transport of soldiers to field hospitals for treatment. Often, communications trenches also housed war engineers. These engineers were responsible for operating and maintaining crucial communications hardware; they were also tasked with surveying enemy lines and ensuring the continued viability of transport operations behind the front-lines.