<P> Very early in the war, British defensive doctrine suggested a main trench system of three parallel lines, interconnected by communications trenches . The point at which a communications trench intersected the front trench was of critical importance, and it was usually heavily fortified . The front trench was lightly garrisoned and typically only occupied in force during "stand to" at dawn and dusk . Between 65 and 90 m (70 and 100 yd) behind the front trench was located the support (or "travel") trench, to which the garrison would retreat when the front trench was bombarded . </P> <P> Between 90 and 270 metres (100 and 300 yd) further to the rear was located the third reserve trench, where the reserve troops could amass for a counter-attack if the front trenches were captured . This defensive layout was soon rendered obsolete as the power of artillery grew; however, in certain sectors of the front, the support trench was maintained as a decoy to attract the enemy bombardment away from the front and reserve lines . Fires were lit in the support line to make it appear inhabited and any damage done immediately repaired . </P> <P> Temporary trenches were also built . When a major attack was planned, assembly trenches would be dug near the front trench . These were used to provide a sheltered place for the waves of attacking troops who would follow the first waves leaving from the front trench . "Saps" were temporary, unmanned, often dead - end utility trenches dug out into no - man's land . They fulfilled a variety of purposes, such as connecting the front trench to a listening post close to the enemy wire or providing an advance "jumping - off" line for a surprise attack . When one side's front line bulged towards the opposition, a salient was formed . The concave trench line facing the salient was called a "re-entrant ." Large salients were perilous for their occupants because they could be assailed from three sides . </P> <P> Behind the front system of trenches there were usually at least two more partially prepared trench systems, kilometres to the rear, ready to be occupied in the event of a retreat . The Germans often prepared multiple redundant trench systems; in 1916 their Somme front featured two complete trench systems, one kilometre apart, with a third partially completed system a further kilometre behind . This duplication made a decisive breakthrough virtually impossible . In the event that a section of the first trench system was captured, a "switch" trench would be dug to connect the second trench system to the still - held section of the first . </P>

The term total war is applied to world war i to capture the idea that the war