Receiving the temporary rank of commodore, Brenton entered the Adriatic with Captain William Hoste's HMS "Amphion" and HMS "Mercury" commanded by Captain Henry Duncan, and attacked the port at Pesaro in April, capturing 13 merchant vessels before blowing up a castle at the harbour entrance. The following month, "Spartan" and "Mercury" entered the port of Cesenatico, destroyed the shore batteries and cut out twelve merchant vessel and burnt another. Shortly afterwards, Brenton was dispatched to the coast of Croatia to assist with the Austrian offensive against the French garrison on the island of Lošinj. After embarking a detachment of Austrian soldiers, Brenton launched an assault on the French defences and captured the island, suffering only three wounded.