The engines that powered the B type Fairmile were the American Hall Scott Marine V12 cylinder petrol engine.
Although originally designed to be powered by 3 of these engines, due to the war time shortage of materials they were only powered by 2.

The H/S engine required 100% octane petrol to perform to their specifications and to last the required time between overhauls. Due to this a wooden vessel with 2000 gallons of high octane fuel on board was a potential Guy Fawkes night. (See Ostend St Valentines Day 1945). Remember the MM and stokers worked side by side with the fuel tanks.