logo

21-inch Torpedo Mk.VIII (Demonstrator)

Manufacturer:  
Model: 21-inch Torpedo Mk.VIII
Years of use: 1927-1999
Known History:

The torpedo was housed at HMS Dolphin, the Royal Navy Submarine School at Gosport and has been sectioned for training purposes. This school closed in 1999 and relocated to HMS Raleigh at Torpoint in Cornwall. The torpedo was destined for a museum in Hong Kong but the deal fell through. About 10 years ago while at a dinner party, James Shopland (a naval historian) was discussing the torpedo and ended up buying it. The trailer was later acquired on ebay.

In WW2, a torpedo like this would have cost as much as a Spitfire.

History:

The Mark VIII was designed around 1925 and was the first British burner-cycle design torpedo. It was used from 1927 on submarines of the O class onwards and motor torpedo boats. The principal World War II version was the improved Mark VIII - 3,732 being fired by September 1944 (56.4% of the total number). The torpedo was still in service with the Royal Navy as late as 1983, and with the Royal Norwegian Navy (Coastal Artillery: Kaholmen torpedo battery at Oscarsborg fortress) until 1993. The Mark VIII was used in two particularly notable incidents:- On 9 February 1945 the Royal Navy submarine HMS Venturer sank the German submarine U – 864 with four Mark VIII torpedoes. This is the only intentional wartime sinking of one submarine by another while both were submerged. On 2 May 1982 the Royal Navy submarine HMS Conqueror sank the Argentine cruiser ARA General Belgrano with three Mark VIII torpedoes during the Falklands war. This is the only sinking of a surface ship by a nuclear-powered submarine in wartime (and only the second sinking of a surface ship by any submarine since the end of WWII).

Operation:

Mark 8 Torpedo Mod 4

This version was wired and connected to the submarine by an umbilical cable which allowed electrical pre-set of depth and direction before launch.

Propulsion System

The torpedo is powered by a 4 cylinder radial engine. Compressed air from the main tank at 2500 psi is fed via a reducer (down to 550 psi) into the engine. Fuel is also added. The fuel was original Broxburn shale oil (home produced) but went on to be paraffin or kerosene.

Starting

The start lever knocked back on launch. This allowed compressed air into the system to start pressurising. Water or compressed air is used to force the torpedo from its tube. The torpedo does not start running until its outside it tube. The propeller would be windmilling to assist t engine start up. Heater starts up to heat pocket in front of motor casing. This heats air before going into reducer to prevent freezing and also heats fuel. Increases engine efficiency. There is no speed control. Engine will run at full power for 4 – 5 mins to give the torpedo a speed of 41 knots and a range of 7000 yds. The engine exhausts via the hollow prop shaft and out through the centre of the propellers. Engine compartment floods to keep engine cool. A flap valve at the side of the engine operates on launch. This starts the heater, allows fuel into the engine and can determine the length of run. If the torpedo did not hit its target it would then sink. German torpedo’s didn’t do this. They floated and became mines.

Steering and Depth Control

There is a hydrostatic valve fitted with a pendulum mechanism to stop the torpedo from porpoising. A spindle would set the hydrostatic valve to control depth but in later models this was electrically set via a small servo motor. The output rod was connected to an air servo valve (not hydraulic oil). The output would push/pull a shaft connected to the horizontal rudder at the rear. Steering was electrically preset (depth and giro angle). Giro is air powered and spins up after launch – high pressure to begin with to get it spinning then low pressure to keep it running. Giro offset could be up to 170 degrees which means torpedo could be fired when not facing direction of travel. There is a hatch under the giro to allow removal for maintenance. The output from the giro controls air at 550 psi to a control motor at the aft end. This is connected to the vertical rudders to control direction.

Dials atop the torpedo

These dials set timers for:- 1. Flasing up the igniters 2. Injecting fuel into the engine 3. Length of run

Warhead

Our ‘warhead’ is actually a ‘blowing head’ which allowed to torpedo to float so that it could be recovered after test firings. It is painted in ‘Dayglo’ orange so it can be seen from great distances. The real warhead would be packed with 750 lb of TNT until 1943 after which 805 lb of Torpex was used. The torpedo would be loaded into the submarine without the ‘pistol’ being fitted. The ‘pistol’ is the detonating mechanism and held safe by a safety pin.

Firing

When fired, water would lift a locking lever allowing a paddle wheel to spin. This would lower the detonator into its pocket. Torpedo could be 600 yds from submarine by now. The detonator is made from very sensitive explosive.

Impact

When it receives an impact of 5g or greater a pendulum delivers an electrical pulse to fire the detonator. This in turn sets off the primary explosive (less sensitive) which in turn sets of the main charge (even less sensitive) of TNT or Torpex.

Proximity

The CCR (coil compensated rod) system is used. This detects the ships magnetic flux which induces a current thus detonating the torpedo. The idea was to detonate 20ft – 30ft below the ship to break its back.

DSC03032_1.JPGimg_8815.jpgDSC03842_1.JPGDSC03845_1.JPGDSC03059_1.JPGDSC03028_1.JPG11536055_10204607157967467_896026115342969334_n.jpg11667357_10204607157407453_5069219010067133686_n.jpg11403132_10204607157607458_1806623256409792468_n.jpgDSC00709_1.JPGGerman20battleship20and20Torpedo20and20us20trim5.jpg11141209_10204607157127446_6191957761982071436_n.jpg11391353_10204607158407478_1823877576074081088_n.jpg