The Fuze Keeping Clock (FKC) was a simplified version of the Royal Navy's High Angle Control System analogue fire control computer.The Gunnery Pocket Book, pp. 153–54, paragraphs 432–35 It first appeared as the FKC MkII in destroyers of the 1938 ,Tribal Class Destroyers, Hodges, p. 27 while later variants were used on sloops, frigates, destroyers, aircraft carriers and several cruisers.Naval Weapons of WW2, Campbell, p. 19 The FKC MkII was a non-tachymetric anti-aircraft fire control computer. It could accurately engage targets with a maximum speed of .
Operation The FKC received vertical reference information from a Gyro Level Corrector and aircraft altitude, range, direction, and speed input information from the Rangefinder-Director, and output to the guns the elevation and deflection data needed to hit the target, along with the correct fuze timing information, so that the shells fired would explode in the vicinity of the target aircraft.Hodges and Friedman, Destroyer weapons of WW2, p. 51 Most guns controlled by the FKC had Fuze Setting Pedestals or Fuze Setting Trays where the correct fuze timing was set on a clockwork mechanism within the AA shell warhead.Hodges and Friedman, Destroyer weapons of WW2, p. 95–96
Development Type 285 radar was an early addition to the FKC system, being fitted on new destroyers from mid-1941 onward, and retrofitted to existing destroyers as time and opportunity permitted.Howse, Radar at sea: The Royal Navy in World War 2 Later variants increased the maximum target speed to ,Destroyer Weapons of WW2, Hodges/Friedman, p. 102 and were combined with Gyro Rate Units (GRU) which gave tachometric capabilities to the system, and radar which greatly improved ranging and rate keeping accuracy.Naval Weapons of WW2, Campbell
Wartime use
The FKC saw extensive use during the war on British Commonwealth naval ships, typically on destroyers and sloops. Prior to the widespread use of radar, optical detection and ranging on high altitude aerial targets was a daunting task, as shown by 's Report of Proceedings, for 3 September 1940:
Occasionally conditions would conspire to favour the surface ships during an aerial attack, as again revealed by HMAS Parramattas Report of Proceedings, for 20 September 1940:
The FKC was used throughout the war and its effectiveness was increased by the use of radar for gunnery and to provide warning against surprise attack, as demonstrated by this account of bringing down a Japanese A6M Zero fighter aircraft (a "HAMP"), in 1944:
Notes
External links The Gunnery Pocket Book, B.R. 224/45, 1945
Illustration of the FKC Mk II