From then until 1808 "Sirius" served in the Mediterranean. On 17 April 1806 at 2pm "Sirius" was five or six leagues off Civitavecchia when Prowse received intelligence that a French force had sailed that morning for Naples. He immediately set out and succeeded in catching up with them just after sunset two leagues from the mouth of the Tiber River. The force consisted of a ship, three corvettes, and five heavy gun-vessels, and they were deployed in line of battle near a dangerous shoal, awaiting "Sirius"s attack. The action commenced at 7pm and lasted for two hours before the French ship leading the flotilla struck. The water had been calm so the French had been able to fire well and "Sirius" herself was too damaged to pursue when the remainder of the French flotilla withdrew; Prowse was also concerned about the risks of pursuit at night in water with shoals.