On 1st September 1865 he was appointed Commanding Royal Engineer officer at Gravesend, to superintend the erection of the new forts to be constructed in that locality for the defence of the Thames. For such a post his active military service, as well as his technical training, eminently suited him; and although there was little promise of excitement about it, the work was distinctly congenial, and offered him a field for showing practical judgment and skill as an engineer. He threw himself into his task with his characteristic energy and enthusiasm. But how far the latter was damped by his prompt discovery that the whole project of the Thames defences was faulty and unsound it is impossible to say, but his attention to his work in all its details certainly showed no diminution or falling off. There were five forts in all to be constructed--three on the south or Kent side of the river, viz., New Tavern, Shornmead, and Cliffe; and two, Coalhouse and Tilbury, on the north or Essex side. An immense sum had been voted by Parliament for their construction, and Gordon was as loud as an officer dare be in his denunciation of this extravagant waste of money as soon as he discovered by personal examination that the three southern forts could be turned into islands, and severed from all communication by an enemy cutting the river bank at Cooling; and also that the northern forts were not merely unprotected in the rear, like those of the Chinese, but completely commanded from the Essex range of hills. Notwithstanding this important discovery, made at the very beginning, the original scheme was prosecuted to the end, with enormous outlay and useless result, for an entirely new system of river defences had to be formed and carried out at a later period. But for these errors Gordon was in no sense responsible, and they would not have been committed if his advice and representations had been heeded.
Mr Arthur Stannard, who was assistant to the manager of the firm which had been intrusted with the contract for the building of these forts, gave in the _Nineteenth Century_ for April 1885 the best account we possess of the manner in which Colonel Gordon discharged his official duties at Gravesend.