A motor torpedo boat is a fast torpedo boat, especially of the mid 20th century. The motor in the designation originally referred to their use of petrol engines, typically marinised aircraft engines or their derivatives, which distinguished them from other naval craft of the era, including other torpedo boats, that used steam turbines or reciprocating steam engines. Later, diesel-powered torpedo boats appeared, in turn or retroactively referred to as "motor torpedo boats" for their internal combustion engines, as distinct from steam powered reciprocating or turbine propulsion. Though other navies built similar petrol-powered craft, the specific designation "motor torpedo boat", abbreviated to "MTB", is generally used for craft of the Royal Navy (RN) and Royal Canadian Navy boats. During the Second World War, the US Navy built several classes of marine V-12-powered PT boat, whose hull classification symbol "PT" stood for "patrol, torpedo", but which were grouped into motor torpedo boat squadrons.<ref>{{Cite web |url=https://www.history.navy.mil/research/archives/digitized-collections/action-reports/wwii-pearl-harbor-attack/motor-torpedo-squadron-one-action-report.html |title=Motor Torpedo Squadron ONE, Report for Pearl Harbor Attack, Naval History and Heritage Command |access-date=29 February 2020 |archive-date=11 August 2020 |archive-url=https://web.archive.org/web/20200811063151/https://www.history.navy.mil/research/archives/digitized-collections/action-reports/wwii-pearl-harbor-attack/motor-torpedo-squadron-one-action-report.html |url-status=dead }}</ref> German diesel-powered torpedo boats of the Second World War were called S-boote (Schnellboote, "fast boats") by the Kriegsmarine and "E-boats" by the Allies. These large craft (well over 100 ft overall) were not known as motor torpedo boats at the time, but later have been grouped with them by some. Italian MTBs of this period were known as Motoscafo Armato Silurante ("MAS boats", torpedo-armed motorboats). French MTBs were known as vedettes lance torpilles ("torpedo-launching fast boats"). Soviet MTBs were known as торпедные катеры (torpyedniye katyery; "torpedo cutters", often abbreviated as TKA). Romanian MTBs were known as vedete torpiloare ("torpedo fast boats"). The role of the motor torpedo boat has been absorbed in modern navies by the fast attack craft. History Torpedo boats were designed for missions that variously involved high speed, operating at night, low speed ambush, and manoeuvrability to allow them to get close enough to launch their torpedoes at enemy vessels. With no significant armour, the boats relied upon surprise and agility at high speed to avoid being hit by gunfire from bigger ships. The Royal Navy started developing particularly small, agile, and fast petrol-powered torpedo boats in the early 20th century, shortly before the beginning of the First World War. Known as coastal motor boats, these were only around . They were joined by the Italian Navy's MAS boats, of displacement.