Trench warfare has become a powerful symbol of the futility of war.[4] Its image is of young men going “over the top” (over the parapet of the trench, to attack the enemy trench line) into a maelstrom of fire leading to certain death, typified by the first day of the Somme (on which the British suffered 57,000 casualties) or the grinding slaughter in the mud of Passchendaele. To the French, the equivalent is the appalling attrition of the "Wringer of Verdun" in which they suffered 380,000 casualties.[5]

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Note added at 59 mins (2010-01-28 17:30:04 GMT)
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http://en.wikipedia.org/wiki/Going_over_the_top

"Going over the top" is a military phrase derived from the trench warfare of the First World War (generally, trench warfare was used on the Western Front). Attacks starting from trenches required infantry to climb over the top of the parapet before they could cross no man's land to attack the enemy trenches. "Going over the top" was an unpopular task; soldiers awaited three blows on a whistle to proceed. One soldier commented "it felt like such a long time waiting to go over the top that many of us expected the war to be over by the time we had climbed on to 'no man's land'". This was used repeatedly during the Great War.