When the British dispatched 400 tanks against the Germans at the Battle of Cambrai in 1917, the result was a draw for the armies--but a win for the tank, following its first major role in combat. But the initial British successes were due to innovations in artillery, not tanks--and tanks didn't keep the Germans from recapturing their losses. Bryn Hammond shows how generals and politicians seduced by the tank's mythical abilities helped create a more mobile army in the following decades.