The "Richelieu"-class ships were powered by four Parsons geared steam turbines and six oil-fired Sural forced-circulation boilers manufactured by Indret for "Richelieu" and by Penhoët and AC de la Loire for "Jean Bart". The Sural boilers were experimental, and were thus a major risk to take with what were to be the most powerful capital ships of the French fleet; they nevertheless proved to be generally reliable in service. Like the "Dunkerque"s, the "Richelieu"s used the unit system of machinery for their propulsion system, which split the machinery into two separate systems. Three boilers were placed in one boiler room, followed by the forward engine room that housed the pair of turbines that drove the outer pair of propellers. Next astern was a second boiler room, followed by a second engine room, which powered the inner pair of screws. The arrangement offered improved damage resistance, since one system could be disabled due battle damage and the other could remain in operation. All four screws had four blades and were in diameter. The boilers were ducted into a single funnel.