As Captain Joseph Denman, one of the most experienced British naval officers to serve in the anti-slave trade blockade of the west African coast, was later to recall, the year 1839 opened ‘an era in the history of the slave trade when for the first time suppression [by the British navy] became possible’. Ships of the Royal Navy were at last empowered to search and capture Portuguese and Brazilian (as well as Spanish) vessels—together with those without nationality—carrying slaves or simply equipped for the trade in southern as well as northern latitudes. Moreover, the activities of the navy—at least on the African side of the Atlantic where Britain's efforts for the suppression of the foreign transatlantic slave trade were still concentrated—were no longer confined to the high seas. Lord Palmerston had already advised the Admiralty that, in the opinion of Sir John Dodson, the Advocate General, if British warships were to enter African waters and rivers it was unlikely that local chiefs would, or were entitled to, claim that their territorial rights had been violated. In 1841 he confirmed that his Act of 24 August 1839 authorised British officers to search and detain slavers found at anchor off ports in Portuguese Africa and in Portuguese African waters: where there were Portuguese authorities in the vicinity prior permission should be sought but, even if it were refused, an officer should not be deterred from doing his duty provided that he did not expose his ship to attack from Portuguese shore batteries.