Difference between revisions of "Leon Torpedo Mine"

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Latest revision as of 09:08, 14 July 2019

Leon Torpedo Mine[1]

The Leon Torpedo Mine was invented by a Swedish naval officer, Captain Karl Oskar Leon. It was an "oscillating mine", cylindrical in shape and of slightly negative buoyancy. It could be deployed from a boat or from a submerged torpedo tube and to oscillate around a preset depth under the action of a small electrically driven propeller without use of mooring cables.

British Testing

In 1913, the Royal Navy had William Beardmore & Company build four of these (in approximately 18-in and 21-in diameters) for testing,[2] and issued a report in 1914.[3]

British Experimental Leon Torpedo Mines[4]
  21-in model 18-in model
Overall Length 5 ft. 10 in. 7 ft. 2-in
Diameter 550mm/20.8 in. 450mm/17.72 in.
Length of pistol horns 11 in.
Length of explosive 2 feet 2 ft. 6.7 in.
# Edison B.S. 2 Cells 17 13
Voltage 21-22 16-17
Battery capacity 40-60 amp. hrs.
Battery Weight 108 lbs. 85 lbs.
Total Weight 668 lbs. 619 lbs.
Casing 0.125 in. steel
Motor H.P. 0.25[5]
Propeller 7.25 in.
Charge weight 220 lbs.

Mode of Operation

Upon being deployed, the weapon would rise to the surface, but an inlet valve would admit water to a fourteen pound ballast tank to prompt it to sink at a mildly negative buoyancy. From here, its behaviour depended on its configuration.

The mine was triggered by one of two pistols. One was connected to four whiskers on the head of the mine which would be actuated by as little as 4.5 pounds of force being applied, and the other was an inertial trigger that employed a 1-in diameter ball. Both were electrical, and interlocked with a six-day spring clock that had a cam by which it could trigger changes in behaviour every six hours — an interval ideal for waiting out unhelpful phases of tidal flow near harbours.

When the mine was active, a propeller driven by an electrical motor would work in conjunction with a hydrostatic valve to bring the mine to a set depth adjustable between 5 and 30 feet about which it would oscillate in a near-neutral buoyant state, within an envelope of about 5 feet in depth.

By different wiring schemes on the back of an access door, four modes of oscillation could be selected, the first two intended for use near harbours:

  1. it could actively oscillate for any duration less than six hours, before beginning an alternation of six hour passive/active states
  2. it could be passive for any duration less than six hours, before beginning an alternation of six hour active/passive states
  3. it could be set to oscillate for for any duration less than six hours before rising to the surface until its battery was exhausted, at which time it would sink to the bottom
  4. it could be be set to oscillate until battery was exhausted, at which time it would sink to the bottom

The Swedish designer felt that the weapons should have only 1.5 pounds negative buoyancy, as this would offer long battery life. The British felt this was too fine a margin; they tested their weapons at two and four pounds negative. They found a five foot range of oscillation resulted, taking about 12 seconds to sink under the negative buoyancy and 17 seconds to rise under the action of the propeller. At four pounds negative buoyancy, the 21-in mine could oscillate for 2.25 hours and the 18-in for 3 hours. At two pounds, the endurances were 8 hours for 21-in and 5.75 hours for 18-in.

The British only conducted one trial of ejecting a mine from a submarine's submerged torpedo tube, and lost the mine. It was presumed that the air impulse damaged the mine's delicate propeller.

It is curious that the battery lives were so short that a single hour phase of active oscillation was nearly the limit of the mine's life cycle.

British Refinements

Leon Torpedo Mine, c. 1915[6]

By 1915, the British had concluded that firing from submerged tubes was not presently a safe operation, and that it should be dropped or rolled overboard. The warhead had been increased to 250 pounds of Amatol, and the clock had been removed outright.[7]

British Leon Torpedo Mine Design of 1915[8]
Overall Length 7 ft. 2-in
Diameter 450mm/17.72 in
Casing 0.125 in. steel
Length of pistol horns 11 in.
# Edison B.S. 2 Cells 13
Voltage 16-17
Battery capacity 40-60 amp. hrs.
Battery Weight 84 lbs.
Total Weight c. 450 lbs.
Motor Power 0.25 H.P.
Propeller Speed 200 RPM
Charge weight 220 lbs.
Oscillation Period c. 12 seconds each way
Oscillation range 5 feet each way
Battery Life 6-8 hours

German Use in the War

The British felt that the German Navy used them in the war, probably from submarines, as several were recovered near the coast with guide strips in place for deployment from torpedo tubes. They differed from the British test articles in that they lacked firing whiskers and only had inertial triggers, and they had a charge of 250 pounds of T.N.T.. Their battery life was judged to be 8 hours. All those found were set to sink at the end of their life; they had been set for 4.75 metres. It was feared that they were likely to be deployed from warships fleeing pursuit, prompting cautions against crossing the wakes of ships being chased down.[9]

See Also

Footnotes

  1. Brassey's Naval Annual, 1914, figure page 318.
  2. Annual Report of the Torpedo School, 1913. p. 76.
  3. Annual Report of the Torpedo School, 1914. pp. 67-70, Plates 38-41.
  4. Annual Report of the Torpedo School, 1914. p. 69.
  5. My photograph is not very clear for this item.
  6. Annual Report of the Torpedo School, 1915. Plate 58.
  7. Annual Report of the Torpedo School, 1915. pp. 153-5.
  8. Annual Report of the Torpedo School, 1915. p. 154.
  9. German Navy: Part IV, Section 3. Torpedoes, Mines, Etc.. pp. 28-9, Plates 41, 42.

Bibliography

  • Admiralty (July, 1917). German Navy: Part IV, Section 3. Torpedoes, Mines, Etc. (C.B. 1182) The National Archives. ADM 186/228.
  • H.M.S. Vernon. (Feb 1914) Annual Report of the Torpedo School, 1913, with Appendix (Wireless Telegraphy). Copy 42 at The National Archives. ADM 189/33.
  • H.M.S. Vernon. Annual Report of the Torpedo School, 1914. Copy 5 at The National Archives. ADM 189/34.