From 1804 up to 1814 Douglas continued to be connected with the educational department of the army. It would be impossible to overestimate the importance of the services which he rendered. He not only instructed candidates for Staff employment by lessons gathered from the past, but deduced, from his own clear perception of things, hints and suggestions which were then entirely new. He had many differences because of this habit with General Zamy, who, like veterans in general, was slow to believe that the tactics and strategy of his own youth could be improved upon. But in 1806 the old man retired, and Douglas, with the rank of lieutenant-colonel, took his place at the head of the establishment. A fresh impulse was immediately given to the course of study. Not surveying only, but pontooning, artillery, and the theory of the whole art of war, were taught, and those brilliant Staff officers sent out who in the Peninsular struggle gave to the Great Duke such efficient support. Sir Howard, however—for he had by this time succeeded by the death of another brother to the baronetcy—yearned for active employment in the field. He applied for and obtained permission to join Sir John Moore’s army, which he overtook just as the retreat from Benevente began; and he shared its fortunes both in the painful marches which it accomplished, and in the battle near Corunna, which enabled it to re-embark without dishonour. By-and-by, when the expedition to the Scheldt was fitted out, Sir Howard prevailed upon the Duke of York to appoint him to the Staff of Lord Chatham’s army as Deputy Quartermaster-General. The enterprise grievously failed; and the loss by disease among the troops and ships’ companies engaged was very severe. But even under such circumstances Sir Howard proved of great service to his chief: for having kept a journal of each day’s proceedings as it occurred, he was able to show, when examined concerning the causes of the failure, that by far the largest share of blame rested with the navy, or rather with the officer whom the Admiralty had placed at its head.