Barr and Stroud Mark II* Fire Control Instruments

Barr and Stroud's Mark II* series of step-by-step fire control instruments were outwardly nearly indistinguishable from the Mark II versions, but their internal wiring and brushes differed. The function would have been identical, and the changes were perhaps to enhance problems maintaining connectivity in Mark II plugs — the most common type of failure particular to that series.

There were a few functional enhancements as well:

• Bearings were expressed a relative bearings and not compass quadrant bearings as under Mark II
• Range rates were expressed in 25 rather than 10 yards/minute steps

Bearing Instruments

Bearing Transmitter Mark II*

Bearing Receiver Mark II*

These were similar to the Mark I instruments, but worked in relative bearings, not compass quadrant bearings. An additional digit drum was fitted to permit angles of 0 to 180 in 1/4 degree increments, and a single remaining shutter located underneath the digital bearing drums could be in either STARBOARD or PORT position (starboard was in the higher position, and so would be visible when the shutter was lowered). I guess that this shutter was also in the raised position when the coil was off.

One small difference was that the transmitter handle had to be pushed in before would engage the drums inside. A spring would keep it out, otherwise. The degree handle was on the right side near the bottom, and the shutter setting handle on the left near the bottom. I am not sure if the degree drums and the shutter position were interconnected, or what behaviour would result if the angle was driven to (or past) its maximum reading.

The Pattern 2607 Transmitter had an integral tell-tale for angle and port/starboard. It was fed by six wires, five of which it passed to the Pattern 2608 Receiver.

The Mark II* Rate of Change transmitter was fundamentally similar, with CLOSING and OPENING on the shutter.

Combined Range Deflection and Order Instruments

Both the Pattern 2596 Combined Receiver and Pattern 2597 Combined Transmitter had 3 glands to admit cables.

Rate Instruments

These minor adaptations (pattern numbers unknown) on the Mark II rate transmitter and receiver replaced the two rightmost digit drums with the standard 00, 25, 50, 75 drum reflecting the Royal Navy's standardisation of units of 25 yards per minute for range rates. The shutter below the digits was also reworded to read OPEN or CLOSE.

Single Range Instruments

The Pattern 2598 Single Range Receiver.

The Pattern 2599 Single Range Transmitter had 2 glands to admit cables.

Single Order Instruments

Pattern 2600 Single Order Receiver Pattern 2601 Single Order Transmitter

See Also

• Barr and Stroud Mark II Fire Control Instruments
• Barr and Stroud Mark III Fire Control Instruments

Bibliography

• 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.