Increasing the knocking limits of existing aviation fuels became a major focus of aero engine development during World War II. By the end of the war, fuel was being delivered at a nominal 150-octane rating, on which late-war aero engines like the Rolls-Royce Merlin 66[22][23] or the Daimler-Benz DB 605DC developed as much as 2,000 hp (1,500 kW).[24][25]