By Oman's own admission, Wellington’s Army, 1809-1814 is a sort of companion to his landmark work, the History of the Peninsular War. On the first page he states,

“While working for the last nine years at the History of the Peninsular War, I have (as inevitable) been compelled to accumulate many notes, and much miscellaneous information which does not bear upon the actual chronicle of events in the various campaigns that lie between 1808 and 1814, but yet possesses high interest in itself, and throws many a side-light on the general course of the war.”

More specifically, this book details the organization, tactics, composition, and leadership of the British army of the Peninsular War, as well as a few interesting sections on miscellaneous subjects such as marching, religion, and punishments.

My favorites chapters were “Sources of Information – the Literature of the Peninsular War” and “Wellington’s Lieutenants”. In the former, Oman discusses the vast quantity of material about the Peninsular War written by its participants. He evaluates Napier’s famous history and provides useful judgments on the myriad of personal memoirs. In particular, I enjoyed this chapter because it gave me several suggestions of books I want to read. The two chapters on Wellington’s Lieutenant’s looked at the most important Generals besides Wellington himself: Hill, Beresford, Graham, Picton, and Crauford.

Even if you have read many books about the Peninsular War, you can still learn much from Wellington’s Army, 1809-1814. The research that went into this book is quite evident, and the appendices are full of useful information regarding the composition of the Peninsular army, as well as containing a full bibliography.