Barr and Stroud Mark IV Fire Control Instruments
Barr and Stroud's Mark IV series of step-by-step fire control instruments were a modest upgrade from the Mark III* series. As they and the Mark III and III* series are outlined in the Handbook for Fire Control Instruments, 1914 but not mentioned in the 1909 edition, Mark IV probably was introduced between 1911 and 1914. 1914 appears most likely, as the series has far less data in that handbook than the two preceding generations.
These were nearly identical to the Mark II.* models.
The Pattern 3139 Bearing Receiver's STARBOARD/PORT shutter had a third face added to the bottom, which was blank and it had no blank/TRAIN shutter. I do not understand why this would be considered an improvement unless the digit display can go all the way up to 360 (or down to -180), and this was intended to be used with the blank face of the shutter on display.
The Pattern 3138 Bearing Transmitter had handles and a lower gearbox.
The Rate Transmitter (of unknown pattern number) was identical to the Mark III except the shutter coils and digital drums are fed their input from without and not directly from the transmitter and shutter switches. This allowed the tell-tale indicators to receive their data from a change-over switch, as though they were an ordinary receiver. This removed the need for a COS to have its own tell-tale indicator in cases where it was going to be placed adjacent to the transmitter anyway.
- 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.