The Fairmile D motor torpedo boat was a type of British Motor Torpedo Boat (MTB) designed by Bill Holt and conceived by Fairmile Marine for the Royal Navy. Nicknamed "Dog Boats", they were designed to combat the known advantages of the German E-boats over previous British coastal craft designs. They were bigger than earlier MTB or Motor Gun Boat (MGB) designs (which were typically around 70 feet) but slower, at 30 knots compared to 40 knots. Many versions were produced or converted from existing boats; MGB, MTB, MA/SB, LRRC and post-war FPB.