In 1938, Rolls-Royce started work on modifying some Merlins which were later to be used in British MTBs, MGBs, and RAF Air-Sea Rescue Launches.
I 1938 begyndte Rolls-Royce at modificere nogle Merlins, som senere blev brugt i britiske motortorpedobåde (MTB), motorkanonbåde (MGB), og RAF Air-Sea redningsbåde.