Seeking active employment, Brenton and a number of other Royal Navy officers accepted commissions to serve in the Royal Swedish Navy which was engaged in operations against Russia in the Russo-Swedish War. Although Brenton arrived too late to take part in the Swedish navy's break-out at the Battle of Vyborg Bay in July 1790, he was present at the Swede's decisive victory at the Battle of Svensksund five days later. Peace was declared soon afterwards and although King Gustav offered his British officers continued employment, Brenton returned to England as mounting tensions between Spain and Britain had increased the likelihood of an imminent declaration of war.