<P> Although technology had dramatically changed the nature of warfare by 1914, the armies of the major combatants had not fully absorbed the implications . The French and German armies adopted different tactical doctrines: the French relied on the attack with speed and surprise, and the Germans relied on firepower, investing heavily in howitzers and machine guns . The British lacked an official tactical doctrine, with an officer corps that rejected theory in favour of pragmatism . </P> <P> While the armies expected to use entrenchments and cover, they did not allow for the effect of defences in depth . They required a deliberate approach to seizing positions from which fire support could be given for the next phase of the attack, rather than a rapid move to break the enemy's line . It was assumed that artillery could still destroy entrenched troops, or at least suppress them sufficiently for friendly infantry and cavalry to manoeuvre . </P> <P> In the face of modern warfare, digging in was standard practice by the start of WWI . To attack frontally was to court crippling losses, so an outflanking operation was the preferred method of attack against an entrenched enemy . After the Battle of the Aisne in September 1914, an extended series of attempted flanking moves, and matching extensions to the fortified defensive lines, developed into the "race to the sea", by the end of which German and Allied armies had produced a matched pair of trench lines from the Swiss border in the south to the North Sea coast of Belgium . </P> <P> Trench warfare prevailed on the Western Front from late 1914 until the Germans launched their Spring Offensive on 21 March 1918 . After the buildup of forces in 1915, the Western Front became a stalemated struggle between equals, to be decided by attrition . Frontal assaults, and their associated casualties, became inevitable because the continuous trench lines had no open flanks . Casualties of the defenders matched those of the attackers, as vast reserves were expended in costly counter-attacks or exposed to the attacker's massed artillery . There were periods in which rigid trench warfare broke down, such as during the Battle of the Somme, but the lines never moved very far . The war would be won by the side that was able to commit the last reserves to the Western Front . </P>

When were the first trenches dug in ww1