This 21 inch (533mm) torpedo was used by the Royal Navy from 1911 through to 1918 (and beyond). Designed and built by the Royal Naval Torpedo Factory, the Mark 2 (Mark II) was operational in 1911 and was modified several time (this is the Mod 5 version, about 1915) before being superseded by 21 inch Mk 4 (Mark IV) torpedo by 1918.
The 4-cylinder Brotherhood engine was capable of being fired from a submarine’s bow torpedo tube, from Battleship side tubes or from above-water launcher mountings on smaller warships. By adjusting the fuel and air flow rates, the Mk 2 could be set to run fast (44.5 knots) to a range of 4,500 yards, or out to 18,500 yards at 19 knots.
The torpedo was was designed to be launched from a flooded tube. Once the air start valve is opened, the air in the pressure vessel is first reduced to a steady 350 psi and then fed to the engine to turn it over and clear the water in the cylinders and crank case. The pistons have a vent hole that connects the cylinder head and the crank case.
The vent hole is closed during the power stroke but open during the return stroke – allowing any water to vent into the crank case. Engine need to be cooled by sea water), so the ignition cartridges are not fired until the engine has rotated a preset number of revolutions using the cold air – this is the Ignition Delay – 4-5 revs for an underwater launch and 20-30 revs for an above water launch. When the fuel is then ignited, the engine accelerates to full power./via: vbbsmyt