On 21 May 1833 he was promoted to the rank of lieutenant, and the following December was appointed to the Excellent, then recently established as a school of gunnery, at Portsmouth, under the command of Captain Thomas Hastings (1790–1870).
From her he was appointed in January 1836 to be gunnery-lieutenant of the Melville with Captain Douglas, and, later on, with Richard Saunders Dundas, under whose command he served in China, and was specially promoted to the rank of commander on 8 June 1841 for his services in the Canton river, and particularly at the capture of the Bogue forts on 26 February 1841.
During 1842, while on half-pay, he studied at the Royal Naval College at Portsmouth; and from September 1844 to May 1846 commanded the Flying Fish on the west coast of Africa.
It is interesting to trace these details of his service under such officers as Hastings, Dundas, and Martin, as explaining and illustrating his peculiar fitness for the appointment which he received in January 1854 to the Illustrious, then commissioned as training ship for landsmen entered into the navy, according to a plan of Sir James Graham's, and who consequently became generally known as ‘Jemmy Graham's novices.’ In his discharge of this new and exceptional duty Harris displayed such ability and resource that when, in 1857, it was determined to give effect to a long-mooted scheme for improving the elementary education and training of young officers, the execution of it was entrusted to Harris, in the first instance on board the Illustrious, from which, on 1 Jan. 1859, he and the cadets were moved to the Britannia, then in Portsmouth harbour, but in November 1861 sent to Portland.
Harris continued to hold this difficult and important post till October 1862, during which time the system of education of naval cadets took form, and was permanently established on its present basis.