After a number of postings, in 1854 he joined the Baltic campaign[1] as one of 106 army sappers who accompanied the Royal Navy fleet.

In the Baltic he took part in the Battle of Bomarsund where, as a corporal, he had charge of the carpenters who laid the platform of a British battery landed on Åland Island.

[1] Leitch was a 34 year old colour-sergeant in the Corps of Royal Engineers, British Army during the Crimean War when the following deed took place for which he was awarded the VC.

On 18 June 1855 at Sebastopol, Crimea, Colour-Sergeant Leitch, after approaching the Redan with the leading ladders, formed a caponniere across the ditch as well as a ramp by fearlessly tearing down gabions from the parapet and placing and filling them until he was disabled from wounds.

[1] Rising to the rank of sergeant major,[2] he finally left the army after 28 years service in the Royal Engineers, of which 17 had been spent abroad.