The Allied attempt to break the stalemate of trench warfare by the 'big pushes' of 1916 led to massively costly battles of attrition. The Germans responded by developing schemes of defence in depth anchored on concrete bunkers; the Allies, by sophisticated artillery tactics in support of infantry assaults, and by the introduction of the tank - at first an accident-prone novelty, but later a front-breaking weapon. On both sides the small, self-reliant, opportunistic infantry unit, with its own specialist weapons, became the basic tool of attack. This second of a fascinating two-part study of the birth of 20th century tactics is illustrated in colour and includes rare photographs.