The new 250 mm bore, 900-1000 rpm Bergen C25:33L medium-speed engine from Rolls-Royce is described. The design philosophy and markets for the engine are outlined. Details are given of the core design elements, time between overhauls, cylinder unit concept and impulse turbocharging. The C-engine was designed for reliability and durability, long service intervals and simple servicing, compactness, economy of operation, ease of installation and maintenance, and inclusion of electronic control and monitoring.