The book sets out to show how in the 20th century the British army has learnt lessons from one war in order to prepare for the next. The story is complex for two reasons. First, the truism that all armies learn lessons from wars, usually the wrong ones, is unhelpful. Experience is one of the cornerstones of doctrine: the key issues are which lessons are drawn, whether they are the right ones, and how they are applied. This is the rationale for the interest of armed forces in military history. Secondly the process is particularly fraught for the British army. Its colonial and counter-insurgency commitments have come between its ‘major’ wars, so disrupting many ideas of continuity.