A new biography of Lord Alanbrooke, following his life from childhood through to his role as Chief Imperial General Staff, shaping Allied strategy in World War II.

Lord Alanbrooke was Churchill's right-hand man during World War II, and as Chief of the Imperial General Staff he had an integral part in shaping the strategy of Britain and the Allies. Despite this crucial role, he is very little known compared to military commanders such as Montgomery, Alexander, Slim, Mountbatten, Patton, or Eisenhower.

This new biography of Lord Alanbrooke uses archival material and his diaries to trace his life, including his experiences in World War I and the development of his military career in the interwar years, with a focus on his post as the Chief of the Imperial General Staff during World War II. Voted the greatest Briton of the 20th century, Churchill has long been credited with almost single-handedly leading his country to victory in World War II.

However without Brooke, a skilled tactician, at his side the outcome might well have been disastrous. Brooke more often than not served as a brake on some of Churchill’s more impetuous ideas. However, while Brooke's diaries reveal his fury with some of Churchill's decisions, they also reveal his respect and admiration for the wartime prime minister.

In return Churchill must surely have considered Brooke one of his most difficult subordinates but later wrote that he was "fearless, formidable, articulate, and in the end convincing". As CIGS, Brooke was integral to coordination between the Allied forces, and so had to wrestle with the cultural strategy clash between the British and Americans.

Comments in his diaries offer up his opinions of both his British and American military colleagues – his negative assessments of Mountbatten’s ability, and acerbic comments on the difficult character of de Gaulle and the weaknesses of Eisenhower. Conversely he was clearly over-indulgent in the face of Montgomery's foibles. Brooke was often seen as a stern and humourless figure, but a study of his private life reveals an little-seen lighter side, a lifelong passion for birdwatching, and abiding love for his family.

The two tragedies that befell his immediate family were a critical influence on his life. Sangster completes this new biography with a survey of the way various historians have assessed Brooke, explaining how he has lapsed into seeming obscurity in the years since his crucial part in the Allied victory in World War II.