His first experiences in the navy were serving on ships that had returned from the Battle of Trafalgar with many badly wounded sailors. In November he was transferred to "Temeraire" and then to "Colossus". He later attended a naval school in Portsmouth. In 1806 he served aboard HMS "Woolwich". While serving on "Woolwich" he travelled to the Cape of Good Hope and to St. Helena. In 1808 he moved to the frigate "Resistance", and in 1809 to the frigate "Cornelia". While serving aboard "Cornelia" he travelled to Bombay. Trelawny's name was entered on the books of HMS "Superb" as volunteer first class in October 1812.