Bunbury Enemy Torpedo Calculator

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Bunbury Enemy Torpedo Calculator[1]
The instrument indicates a turn to port of about 23 degrees is required to clear enemy torpedo threat.

The Bunbury Enemy Torpedo Calculator was a defensive Torpedo Control instrument conceived and tested alongside the similar Crace Enemy Torpedo Calculator in 1914-1916.[2] It was created by Lieutenant (T) Evan C. Bunbury.[3]

Its functions could be worked out using a Battenberg Course Indicator, a Torpedo Control Disc or a Torpedo Director Pattern 2006 or Pattern 2392, but the importance of quick decisions as regard enemy torpedo attack merited custom treatment.[4]

Design and Use

The device was circular and intended to be aligned along own ship's keel, marked with relative bearings around its edge. An extension carried forward, and three bars were fitted:[5]

  • Enemy Bar was marked in range and was rotated to point at the enemy
  • Enemy Torpedo Bar was graduated in range
  • Ship Bar representing own ship's travel during torpedo's time-of-flight

Different Ship Bars were provided for each type of enemy torpedo, and they were marked in two scales: knots and yards for other ships astern or ahead of own whose safety might also be considered. The zero points of the scales were shifted for easier construction.

The user would:

  • select and fit the proper Ship Bar for the enemy torpedo in use
  • clamp the outer block to speed of own ship
  • set and clamp Enemy Torpedo Bar at maximum range of enemy torpedo
  • adjust Enemy Bar to range and bearing of enemy
  • if reading edge of Ship Bar is on side of fore-aft line away from enemy, the torpedo can reach own ship and course must be altered as shown by the Ship Bar

To consider the safety of other ships in line with own ship, user would loosen the centre clamp and slide the Ship Bar through the pivot to the line end's distance ahead or astern of own ship and examine whether a turn away was required.

History and Deployment

Six examples of both the Crace and Bunbury devices were manufactured for testing with flagships. The six Bunbury units were to be tried in H.M.S. Emperor of India, Iron Duke, Lion, Marlborough, Barham, and Orion. The device was described in the Handbook for Torpedo Control, 1915 and in a special pamphlet.[6]

The trials were completed in 1917, and it was decided that there was little to differentiate between Crace and Bunbury alternatives.[7]

See Also


  1. Handbook of Torpedo Control, 1916. Plate 23.
  2. Annual Report of the Torpedo School, 1915. p. 60.
  3. Bunbury Service Record. The National Archives. ADM 196/125/412.
  4. Handbook of Torpedo Control, 1916. p. 42.
  5. Handbook of Torpedo Control, 1916. p. 42.
  6. Annual Report of the Torpedo School, 1915. p. 60.
  7. Annual Report of the Torpedo School, 1917. p. 200.


  • Admiralty, Gunnery Branch (1917). Handbook of Torpedo Control, 1916. C.B. 302. Copy No. 141 at The National Archives. ADM 186/381.
  • H.M.S. Vernon. Annual Report of the Torpedo School, 1914. Copy 5 at The National Archives. ADM 189/34.
  • H.M.S. Vernon. (Jan 1916) Annual Report of the Torpedo School, 1915. C.B. 1166. Copy 1025 at The National Archives. ADM 189/35.