# Crace Enemy Torpedo Calculator

Crace Enemy Torpedo Calculator[1]

The Crace Enemy Torpedo Calculator was a defensive Torpedo Control instrument conceived by then-Lieutenant (T) John Gregory Crace around 1912 and tested alongside the similar Bunbury Enemy Torpedo Calculator in 1914-1916.[2]

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.[3]

## Design and Use

The Crace instrument had the following parts as labelled in the drawing to right:[4]

• a torpedo disc, "A", graduated in circles of 500 yards extending to the maximum range of the enemy torpedo, centered on own ship
• a cursor, "B", moved by a screw shaft turned by a knob to set the distance own ship would travel during time-of-flight of the torpedo.
• a sliderule, "C", to help determine the distance to move the cursor based on enemy range and speed of enemy torpedo
• a sliding bar, "D", to show up to 6 ships astern or ahead at 2.5 cable spacing
• a range bar, "E", mounted on the cursor and graduated up to 20,000 yards, able to rotate to enemy bearing

The user would:[5]

1. set the slide rule to range and speed of enemy torpedo
2. set cursor position by noting distance travelled by own ship at its speed as indicated on sliderule
3. set the pointer of sliding bar to the ship in the line to be considered
4. set the range bar to the enemy bearing
5. observe the indicated range on the range bar where it cuts the torpedo circle If the present range is less than this, the enemy is in torpedo range.

To discover how much of a turn is required to escape from torpedo range, the user could note how far he had to rotate the range bar until the indicated threat is no more.

## History and Deployment

Six examples of both the Crace and Bunbury devices were manufactured for testing with flagships. The six Crace units were to be tried in H.M.S. Emperor of India, Invincible, St. Vincent, H.M.A.S. Australia, H.M.S. King George V and Princess Royal. 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]

## Footnotes

1. Handbook of Torpedo Control, 1916. Plate 24.
2. Annual Report of the Torpedo School, 1915. p. 60.
3. Handbook of Torpedo Control, 1916. p. 42.
4. Handbook of Torpedo Control, 1916. pp. 43-44.
5. Handbook of Torpedo Control, 1916. p. 44.
6. Annual Report of the Torpedo School, 1915. p. 60.
7. Annual Report of the Torpedo School, 1917. p. 200.

## Bibliography

• {HTC1916}}
• 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.