# MacNamara's Speed and Course of Enemy Indicator

MacNamara's Speed and Course of Enemy Indicator was a torpedo control device the Royal Navy tried and set aside in 1909-1910.

## Function

Its function is described in the Annual Report of the Torpedo School, 1910.[1] Briefly, the device was quite a bit like a Dumaresq, but was likely flatter. It had a pair of round discs of equal diameter whose diameter was proportional to the supposed (equal) range of the friendly and enemy torpedoes. The user set up the following inputs:

1. Own speed and course (this arm was fixed along your keel line - you would rotate an outer ring to set your heading)
2. Enemy's speed and course (as in a dumaresq, this assembly was carried on the own speed slider)
3. Bearing and distance to enemy
4. Range and speed of the torpedoes (both being assumed the same)

If the disc borne on the enemy slider covered the center of the device, the moment when torpedoes capable of reaching their target had arrived.

## Development and Experience

In 1908, the original version of this was tested and reported on unfavourably. Apparently, it required two observations to be taken exactly a minute apart.[2][3]

In 1909 a modified version was crafted by Vernon which permitted two observations to be taken at any interval and extended a range limit on those from 4,000 yards to 8,000 yards. This version, along with a similar device proposed by Naval Instructor Veater were to receive sea trials,[4] but Veater's was apparently dropped without more than cursory testing.[5]

While an initial trial at a 1909 test torpedo battle practice seemed encouraging. The modified instrument was tested in Bellerophon in 1910. The report criticised the need to apply bearings taken from a separate compass, the inability to apply bearings within 15 degrees of own centerline, and that the course of enemy bar and own ship bar bound up in certain configurations. It was seen as slow and complex and its results unreliable. Bulwark received the instrument, and also had little nice to say about it in practical terms.[6]

## Footnotes

1. Annual Report of the Torpedo School, 1910. p. 34.
2. Annual Report of the Torpedo School, 1908. p. 15.
3. Annual Report of the Torpedo School, 1909. p. 22.
4. Annual Report of the Torpedo School, 1909. p. 22.
5. Annual Report of the Torpedo School, 1910. p. 34.
6. Annual Report of the Torpedo School, 1910. p. 34.

## Bibliography

• H.M.S. Vernon. Annual Report of the Torpedo School, 1909, with Appendix (Wireless Telegraphy). Copy 7 at The National Archives. ADM 189/29.
• H.M.S. Vernon. Annual Report of the Torpedo School, 1910, with Appendix (Wireless Telegraphy). Copy 436 at The National Archives. ADM 189/30.