Colomb entered the navy in 1846, and served first at sea off Portugal in 1847; afterwards, in 1848, in the Mediterranean, and from 1848 to 1851 as midshipman of the "Reynard" in operations against piracy in Chinese waters; as midshipman and shipmate of the "Serpent" during the Burmese War of 1852–53; as mate of the "Phoenix" in the Arctic Expedition of 1854; as lieutenant of the "Hastings" in the Baltic Sea during the Crimean War, taking part in the attack on Sveaborg.