mines. Secondary armament would have been provided by light machine guns, such as the Lewis gun. The CMBs were designed by Thornycroft, who had experience in small fast boats. Engines were not proper maritime internal combustion engines (as these were in short supply) but adapted aircraft engines from firms such as Sunbeam and Napier. A total of 39 such vessels were built. In 1917 Thornycroft produced an enlarged overall version. This allowed a heavier payload, and now two torpedoes could be carried. A mixed warload of a single torpedo and four depth charges could also be carried, the depth charges released from individual cradles over the sides, rather than a stern ramp. Speeds from were possible, depending on the various petrol engines fitted. At least two unexplained losses due to fires in port are thought to have been caused by a build-up of petrol vapour igniting. Italian torpedo boats sank the Austrian-Hungarian in 1917, and in 1918. During the civil war in Russia, British torpedo boats made raids on Kronstadt harbour damaging two battleships and sinking a cruiser. Such vessels remained useful through World War II. The Royal Navy's Motor Torpedo Boats (MTBs), Kriegsmarine 'S-Boote' (Schnellboot or "fast-boat": British termed them E-boats), (Italian) M.A.S. and M.S., Soviet Navy and U.S. PT boats (standing for Patrol Torpedo) were all of this type. A classic fast torpedo boat action was the Channel Dash in February 1942 when German E-boats and destroyers defended the flotilla of , , and several smaller ships as they passed through the Channel. By World War II torpedo boats were seriously hampered by higher fleet speeds; although they still had a speed advantage, they could only catch the larger ships by running at very high speeds over very short distances, as demonstrated in the Channel Dash. An even greater threat was the widespread arrival of patrol aircraft, which could hunt down torpedo boats long before they could engage their targets. During World War II United States naval forces employed fast wooden PT boats in the South Pacific in a number of roles in addition to the originally envisioned one of torpedo attack. PT boats performed search and rescue, reconnaissance, ferry and courier work as well as attack and smoke screening duties. They took part in fleet actions and they worked in smaller groups and singly to harry enemy supply lines. Late in the Pacific War when large targets