He became what was known at that time as a gunner's lieutenant in 1857, and from 1859 to 1863 he served as flag-lieutenant to Rear-Admiral Sir Thomas Pasley at Devonport. Between 1858 and 1868 Colomb was employed in home waters on a variety of special services, chiefly connected with gunnery, signalling and the tactical characteristics and capacities of steam warships. From 1868 to 1870 he commanded HMS "Dryad" in the Persian Gulf region and was engaged in the suppression of the slave trade, particularly around Zanzibar and Oman. His book "Slave-catching in the Indian Ocean: A record of naval experiences" was published by Longmans in London in 1873, an interesting and informative account, one distinguished by a studied moderation.