[3] He joined the Royal Navy as a volunteer, and saw service off the Portuguese and Spanish coast, in the West Indies and in the Mediterranean.

Promoted to Lieutenant in August 1841, he served in HMS Hazard in the 1842 war with China, before the ship was posted to New Zealand.

At Kororāreka in the early morning of 11 March 1845, Commander Robertson, with a party of 45 sailors and marines, repulsed the first attack of the Battle of Kororāreka from Kawiti, Pumuka and their party of some 200 warriors, at Christ Church and along Matavia Pass.

[2] In 1849, he was appointed to the command of HMS Cygnet stationed on the West Coast of Africa, where he spent a year involved in the suppression of the Atlantic slave trade, capturing a number of slave ships.

[9][10] In 1851 he became an Inspecting Commander in Her Majesty's Coastguard, until 1858 when he was promoted to the rank of Captain.