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HACS

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HACS, an acronym of High Angle Control System, was a British anti-aircraft fire-control system employed by the Royal Navy from 1931 onwards and used widely during World War II. HACS calculated the necessary "aim off" required to place an explosive shell in the location of a target flying at a known height, bearing and speed.

Development

The earliest versions of the HACS were not computer predictive, or "tachymetric" systems, which was a flaw but the RN moved quickly to bring the HACS up to date and by mid 1941 it was probably the best naval AA fire control system in the world[1] However the system still had severe limitations as even the highly touted USN Mk 37 system in 1944 needed an average of 1,000 rounds of 5-inch ammunition fired per kill[2]. In 1940 the Gyro Rate Unit (GRU) was added to the HACS system, an analogue computer capable of directly calculating target speed and direction[3], converting the HACS into a tachymetric system[4]. Also in 1940, radar ranging was added to the HACS[5]. The GRU and its associated computer, the Gyro Rate Unit Box (GRUB) no longer assumed straight and level flying on the part of the target. RN destroyers were hampered by the lack of good dual-purpose weapons suitable for ships of destroyer size; for much of the war 40° was the maximum elevation of the 4.7 inch guns equipping such ships, which were consequently unable to engage directly attacking dive bombers, although they could provide barrage fire to protect other ships from such attacks[6]. Destroyers did not use HACS, but rather the Fuze Keeping Clock (FKC), a simplified version of HACS[7]. Starting in 1938 all new RN destroyers, from the Tribal Class onwards, were fitted with a FKC and continuous prediction fuse setting trays for each main armament gun[8]. WWII experience from all navies showed that dive bombers could not be engaged successfully by any remote computer predictive AA system using mechanical fuzes[9] due to the lag time in the computer and the minimum range of optical rangefinders[10]. RN destroyers suffered from a lack of short range, rapid fire, AA with which to engage dive bombers.

By May 1941, RN cruisers, such as HMS Fiji, were engaging the Luftwaffe with stabilized HACS IV systems with GRU/GRUB and Type 279 Radar with the Precision Ranging Panel, which gave +/- 25 yd accuracy out to 14,000 yds. HMS Fiji was finally sunk after running out of AA ammunition but her HACS IV directed 4-inch AA gun battery fended off Luftwaffe attacks for many hours[11]. Demonstrating the RN's rapid strides in naval AA gunnery, in May 1941, HMS Prince of Wales (PoW) went to sea with HACS IVGB, with full radar ranging systems, and no less than 9 AA associated fire control radars: four Radar Type 285, one on each High Angle Director Tower (HADT) and four Radar Type 282, one on each Mk IV QF 2 pdr "pom pom" director, and a long range Radar Type 281 Warning Air (WA) radar which also had precision ranging panels for aerial and surface targets[12]. This placed HMS Prince of Wales in the forefront of naval HA AA fire control systems at that time. In August and September 1941, HMS Prince of Wales demonstrated excellent long range radar directed AA fire during Operation Halberd[13]. However, by December 1941, PoW's AA FC radars had become unserviceable due to the extreme heat and humidity in Malayan waters and her 2 pdr ammunition had deteriorated badly as well[14].

HACS used various director towers that were generally equipped with Type 285 as it became available. This metric wavelength system employed six yagi antennas that could take ranges of targets, and take crude readings of bearings and altitude using a technique known as "lobe switching". It could not however "lock on" to targets, and therefore was unable to provide true blindfire capabilities, which no other navy was able to do until the USN developed advanced radars in 1944 using technology transfers from the UK. This situation was not remedied until the introduction of the HACS Mark VI director in 1944 that was fitted with centimetric Radar Type 275. Another improvement was the addition of Remote Power Control (RPC), in which the anti-aircraft guns automatically trained with the director tower, with the necessary changes in bearing and elevation to allow for convergent fire. Previously the gun crews had to follow mechanical pointers that indicated where the director tower wanted the guns to train.

HACS systems in use or planned in August 1940

HACS Directors fitted to ships in a document dated as "revised Aug 1940"[15]:

  • HACS III: ABC transmission, AV cradle for 15ft HF/RF. Introduced Mk III table.

HMS Ajax, Galatea, Arethusa, Coventry, HMAS Hobart, Sydney, Perth

  • HACS III*: Similar to MarkIII but with larger windscreen and space for a rate officer.

HMS Penelope, Southampton, Newcastle, Malaya, Hood*, Australia*, Nelson*, Royal Sovereign*, Barham*, Resolution*, Cairo*, Excellent (gunnery training school)*, Revenge*, Calcutta*, Carlisle*, HMS Curacoa|Curacoa]]*, Exeter*, Adventure*, Warspite*. Ships marked with * had roll stabilization for layer.

  • HACS III*G as mark III but fitted with GRU and roll stabilization for the layer. (probably mentioned as planned upgrades for previous Mk III directorsVorlage:Fact)
  • HACS IV: Similar to MkIII but with circular screen, magslip transmission and roll stabilization for the layer. Introduced Mk IV table.

HMS Birmingham, Sheffield, Glasgow, Aurora, Liverpool, Manchester, Gloucester, Dido, and Fiji classes, Forth, Maidstone, Renown, Valiant, Illustrious, Formidable and Ark Royal.

  • HACS IV G: Mk IV with Gyro rate unit.

Dido class and Fiji classes.

  • HACS IV GB: Mk IV and fitted with GRU and complete stabilization in laying and training, Keelavite system of power training.

HMS King George V and Prince of Wales, Dido and Fiji classes.

  • HACS V: Improved design, partially enclosed, complete stabilization for elevation and training. Keelavite system of power training, and GRU. Duplex 15ft HF/RF. Uses Mk IV table.

HMS Duke Of York, Anson and Howe.

  • HACS V* :As Mk V but single HF/RF and raised HF/RF compared to Mk V. [16]

HMS Indomitable, Implacable and Indefatigable.

See also

Notes

Vorlage:Reflist

References

  1. ↑ Inferred due to the RN's addition of radar ranging and tachometric target motion prediction to the system. The RN was the first navy to adopt dedicated FC AA radars.
  2. ↑ Naval Weapons of WW2, Campbell, P106
  3. ↑ HACS III Operating Manual Part 1, paragraph 56,61
  4. ↑ Weapon Control in the Royal Navy 1935-45, Pout, p104, from The Application of Radar and other Electronic Systems in the Royal Navy in WW2 (Kingsley-editor)
  5. ↑ Weapon Control in the Royal Navy 1935-45, Pout, p97
  6. ↑ Tribal Class Destroyers, Hodges, p27
  7. ↑ Naval Weapons of WW2, Campbell, p19
  8. ↑ Tribal Class Destroyers, Hodges, p27
  9. ↑ Summary of USN and RN gunnery reports. For example USS Enterprise reported her Mk 33 AAFC system as "ineffective" against dive bombers. U.S.S. ENTERPRISE CV6/A16-3/(10-My)
  10. ↑ HACS III Operating Manual Part 2
  11. ↑ THE TRUE EXPERIENCES OF MR LEONARD CHARLES EADES DURING THE SECOND WORLD WAR, from the HMS Fiji Association.
  12. ↑ The Development of Radar Equipments for the Royal Navy, Kingsley, p383.
  13. ↑ The Royal Navy and the Mediterranean Convoys. A Naval Staff History, p26
  14. ↑ Battleship: The Loss of the Prince of Wales and the Repulse, Middlebrook
  15. ↑ Appendix one, Classification of Director Instruments, see external links.
  16. ↑ Uses FKC AAFC table according to Campbell.
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