Among many publications, he produced a much-used monograph on the Hundred Years' War and the leading biography of King Henry V. Allmand was born into a Catholic family and raised in Hampstead, London.
Allmand, who held a Chair in Chemistry at King's College, London until 1950, having early in his career during World War I carried out important work on the use of gas.
Indeed, Allmand never strayed far from sources, whether printed or archival, and this familiarity with their uses and abuses made him, among much else, an expert editor of the work of others, most notably volume 7 of the New Cambridge Medieval History.
This work goes far beyond the orthodox Shakespeare-dominated image of a king at war and places this complex monarch in an appropriate context of, for example, wide-ranging respect from chroniclers and contemporaries for the good governance and law and order considered essential to successful medieval kingship.
Among other aspects of his research interest were concerns for the non-combatant, and in particular, taking a lead from H J Hewitt's innovative The Organisation of War under Edward III in what might be termed the logistics and practicalities of how medieval warfare were conducted and changed across two centuries.
His kindness towards and encouragement of younger scholars were, to deploy an overused term, legendary, and his wisdom is regularly cited by many historians with an interest in Anglo-Norman and Anglo-French themes such as Professor Anne Curry.
His final collection of articles, brought together as Aspects of War in the Late Middle Ages, included a number of pieces translated by Allmand from French to English.