Barr and Stroud Mark III Fire Control Instruments

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Barr and Stroud's Mark III series of step-by-step fire control instruments were a modest upgrade from the Mark II* series. As they and the Mark III* and Mark IV series are outlined in the Handbook for Fire Control Instruments, 1914 but not mentioned in the 1909 edition, Mark III probably was introduced between 1910 and 1912. Some of the instruments, at least the Single Range Receiver, were still being manufactured in 1919.[1].

With the sole exception of the Single Range Receiver which was now customized for use reporting range cuts to the T.S., the Mark III instruments differed from their predecessors only in their wiring interface. Whereas the Mark II housings each required 2 or 3 individual cables to enter, the Mark III devices consolidated their wiring to receive just a single multi-core cable through a gland. I presume that the outward appearance and function was otherwise identical to the earlier instruments.

Combined Range Deflection and Order Instruments

The Pattern 3141 Combined Receiver and Pattern 3140 Combined Transmitter each accepted a 12-core cable through a single gland.[2]

Single Range Instruments

The Pattern 3142 Single Range Receiver had a shutter which normally obscured the indicated range. A "range cut" button at the rangefinder could be depressed to energize a coil which would flip the shutter aside to reveal the range reading. The shutter remains in a catch until such time as the transmitter changes the range it is signalling. A lever on the left of the receiver could be used to lock the shutter in the open position if desired. This feature rendered unnecessary the use of a separate buzzer circuit which was apparently used with earlier instruments but removed around 1914.[3]

Those instruments with the shutter were dubbed Pattern 3142A or 3142B. In 1919, it was decided that the shutter should be removed in units of future manufacture, to be replaced by a "cut" indicating lamp on the face of the device, energised by the same wire as for the shutter coil.[4]

A twisted knob on the right side of the receiver could apply a differential range in increments of 25 yards up to a maximum of 1000 yards up or down. The intent here was to permit rangefinders to be "biased" into agreement or to account for differences between their location and that of the gun platform being directed.

This instrument had 2 apertures rather than just one. The second one indicated the correction reading being applied.

The Pattern 3132 Single Range Transmitter accepted a 5-core cable through a single gland.[5]

Single Order Instruments

The Pattern 2604 Single Order Receiver and Pattern 2605 Single Order Transmitter were similar to the order component of the combined transmitter, with the indicator of the orders on the front face. Like the other model, it had space for 10 orders. No indication in the handbook reveals what the orders were. It is likely that the combined instruments only utilised 4 or so of their 10 command slots. The front face of the transmitter was somewhat redundant, as it had the list of commands with the present on pointed to by an indicator on a rack and pinion and yet the lower portion of the enclosure had a receiver element whose drum provided a mechanical tell-tale of the same selection. The mechanical tell-tale prevented the transmitter from rolling cyclically.

Rate Instruments

The Pattern 2960 Rate Receiver and Pattern 2961 Rate Transmitter Were mostly as the Mark II* design, but the shutter has a third position which would be blank, and the other faces have been reworded again to OPENING and CLOSING.

Bearing Instruments

These were similar to the Mark II* instruments in that they communicated a relative bearing angle in quarter degree increments, but a second shutter was added which was blank on the high position and marked "TRAIN" in the lower space. This shutter, then, could emphasize that the indicated bearing was not just a declarative but an imperative -- the mount was to train to match the indicated angle.

The arrangement placed the new shutter at the top of the housing of the Pattern 2606 Bearing Receiver, with the STARBOARD/PORT shutter below it and the degree readout at the bottom. Beneath all indicators was the switching rotors and handles. The right side had a large degree-setting handle (again with a spring-loaded design as in the Mark II* design), and the left side had two smaller handles for setting the position of the shutters.

As before, the Pattern 2607 Bearing Transmitter had the tell-tale integrated into its housing, and the receiver appeared like a shorter transmitter (lower gearbox and handles omitted).

See Also


  1. Annual Report of the Torpedo School, 1919. p. 253.
  2. Handbook for Fire Control Instruments, 1914. p. 25.
  3. Annual Report of the Torpedo School, 1914. p. 75, citing G. 21305/13/2835 of 3/2/14).
  4. Annual Report of the Torpedo School, 1919. p. 253.
  5. Handbook for Fire Control Instruments, 1914. p. 25.


  • H.M.S. Vernon. Annual Report of the Torpedo School, 1903, with Appendix (Wireless Telegraphy). Copy 478 at The National Archives. ADM 189/23.
  • H.M.S.O., London Torpedo Drill Book, 1905 (Corrected to December, 1904). Copy in Tony Lovell's library.
  • H.M.S.O., London Torpedo Drill Book, 1908 (Corrected to December, 1907). Copy in Tony Lovell's library.
  • H.M.S.O., London Torpedo Drill Book, 1912 (Corrected to April, 1912). Copy in Tony Lovell's library.
  • H.M.S.O., London (1914). Torpedo Drill Book, 1914 (Corrected to May 15) Copy in Tony Lovell's library.
  • Admiralty, Gunnery Branch (1910). Handbook for Fire Control Instruments, 1909. Copy No. 173 is Ja 345a at Admiralty Library, Portsmouth, United Kingdom.
  • Admiralty, Gunnery Branch (1914). Handbook for Fire Control Instruments, 1914. G. 01627/14. C.B. 1030. Copy 1235 at The National Archives. ADM 186/191.