Pyronaut was the third fire boat to work in Bristol's City Docks. She was built in 1934 at Charles Hill & Sons shipyard and designed to be able to pass under every bridge in the harbour without the need to open them. She could to work between Cumberland Basin and Hanham weir, the entire extent of the port estate in the city. Originally named Phoenix II, she was renamed in 1938, the new name being suggested by the teenage son of the Chair of the Watch Committee who was studying Greek at the time. It was hard for land-based engines to reach ships and buildings and so Pyronaut fought numerous peacetime fires before spending the early part of World War 2 in action almost every time that the Luftwaffe bombed the city. After the war, she reverted to peacetime duties, attending the major blazes at the Hippodrome, St Annes Board Mills, Colston Hall and Rowe Brothers lead works in the 1940s and 50s. She also deputised for the Avonmouth fire boat once a year when it went for maintenance, and spent several days there in 1951 when the largest peacetime fire to that date broke out in the oil tanks. At the end of the 1960s she was re-equipped with new engines and pumps, but the speedy decline of shipping in the City Docks and the greater ease with which land-based engines could get to fires meant that she was sold out of the fire service in 1973.