A History of the British Cavalry 1816-1919 Volume 8: The Western Front, 1915-1919 by The Marquess of Anglesey, FSA.
Lord Anglesey, a very prominent historian, has had many interests besides the cavalry. When he set out to write Volume 8 of his History, he was of the common opinion that cavalry had seen its best days and long outlived its usefulness by the onset of trench warfare.
In the course of his research he came to change his opinion. In this regard his conclusions are similar to those of David Kenyon (Horsemen in No Man’s Land; see my blog post of 12 January 2013).
In the preface Anglesey writes as follows: “More important than any of this (referring to relatively light cavalry casualty figures early in the Great War) was the truly vital part played by the mounted troops of the BEF at the worst moments of crisis. Acting as a ‘fire brigade’ they time and again stopped up gaps as only the sole speedily movable element of the force could do. It is not too much to claim that on a number of occasions catastrophes of major dimensions were averted by such action.”
It is also sadly true, as posited by David Kenyon, that by the end of the war the numbers of cavalry killed and wounded were right up there with the infantry.