Barr and Stroud Mark IV Fire Control Instruments
Barr and Stroud manufactured a large and evolving family of Step-by-Step Fire Control Instruments to convey ranges, deflections, orders and similar information throughout a ship. By 1909, 2 main generations and one minor generation had been introduced. By 1914, another 2 main generations and a minor generation had been introduced.
Mark IV Instruments
Mark IV Bearing Instruments
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.
Mark IV Rate Instruments
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 t o be placed adjacent to the transmitter anyway.
- 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.