![HMS Scylla 1942 IWM FL 2932](https://upload.wikimedia.org/wikipedia/commons/c/c8/HMS_Scylla_1942_IWM_FL_2932.jpg)
High Angle Control System (HACS) was a British
anti-aircraft
Anti-aircraft warfare, counter-air or air defence forces is the battlespace response to aerial warfare, defined by NATO as "all measures designed to nullify or reduce the effectiveness of hostile air action".AAP-6 It includes surface based, ...
fire-control system
A fire-control system (FCS) is a number of components working together, usually a gun data computer, a director, and radar, which is designed to assist a ranged weapon system to target, track, and hit a target. It performs the same task as a ...
employed by the
Royal Navy
The Royal Navy (RN) is the United Kingdom's naval warfare force. Although warships were used by English and Scottish kings from the early medieval period, the first major maritime engagements were fought in the Hundred Years' War against F ...
from 1931 and used widely during
World War II
World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...
. HACS calculated the necessary
deflection
Deflection or deflexion may refer to:
Board games
* Deflection (chess), a tactic that forces an opposing chess piece to leave a square
* Khet (game), formerly ''Deflexion'', an Egyptian-themed chess-like game using lasers
Mechanics
* Deflection ...
required to place an explosive shell in the location of a target flying at a known height, bearing and speed.
Early history
The HACS was first proposed in the 1920s and began to appear on
Royal Navy
The Royal Navy (RN) is the United Kingdom's naval warfare force. Although warships were used by English and Scottish kings from the early medieval period, the first major maritime engagements were fought in the Hundred Years' War against F ...
(RN) ships in January 1930, when HACS I went to sea in . HACS I did not have any stabilization or power assist for director training. HACS III which appeared in 1935, had provision for stabilization, was hydraulically driven, featured much improved data transmission and it introduced the HACS III Table. The HACS III table (computer) had numerous improvements including raising maximum target speed to 350 knots, continuous automatic fuze prediction, improved geometry in the deflection Screen, and provisions for gyro inputs to provide stabilization of data received from the director. The HACS was a ''control system'' and was made possible by an effective data transmission network between an external gun director, a below decks fire control computer, and the ship's medium calibre
anti-aircraft
Anti-aircraft warfare, counter-air or air defence forces is the battlespace response to aerial warfare, defined by NATO as "all measures designed to nullify or reduce the effectiveness of hostile air action".AAP-6 It includes surface based, ...
(AA) guns.
Development
Operation
![HACS deflectionscreen in operation](https://upload.wikimedia.org/wikipedia/commons/7/73/HACS_deflectionscreen_in_operation.jpg)
The bearing and altitude of the target was measured directly on the ''UD4 Height Finder/Range Finder'', a
coincidence rangefinder
A coincidence rangefinder or coincidence telemeter is a type of rangefinder that uses mechanical and optical principles to allow an operator to determine the distance to a visible object. There are subtypes split-image telemeter, inverted image, ...
located in the ''High Angle Director Tower'' (HADT). The direction of travel was measured by aligning a
binocular
Binocular may refer to:
Science and technology
* Binocular vision, seeing with two eyes
* Binoculars, a telescopic tool
* Binocular microscope, binocular viewing of objects through a single objective lens
Other uses
* Binocular (horse), a thoroug ...
graticule
Graticule may refer to:
* An oscilloscope graticule scale
* The reticle pattern in an optical instrument
* Graticule (cartography), a grid of lines on a map
See also
* Grid (disambiguation)
Grid, The Grid, or GRID may refer to:
Common us ...
with the target aircraft fuselage. The early versions of HACS, Mk. I through IV, did not measure target speed directly, but estimated this value based on the target type. All of these values were sent via
selsyn
A synchro (also known as selsyn and by other brand names) is, in effect, a transformer whose primary-to-secondary coupling may be varied by physically changing the relative orientation of the two windings. Synchros are often used for measuring ...
to the HACS in the ''High Angle Calculating Position'' (HACP) located below decks. The HACS used these values to calculate the ''range rate'' (often called ''rate along'' in RN parlance), which is the apparent target motion along the line of sight. This was also printed on a paper plot so that a range rate officer could assess its accuracy.
This calculated range rate was fed back to the UD4 where it powered a motor to move prisms within the UD4. If all the measurements were correct, this movement would track the target, making it appear motionless in the sights. If the target had apparent movement, the UD4 operator would adjust the range and height, and in so doing would update the generated range rate, thereby creating a feedback loop which could establish an estimate of the target's true speed and direction. The HACS also displayed the predicted bearing and elevation of the target on indicators in the Director tower, or on later variants, the HACS could move the entire Director through
Remote Power Control so that it could continue to track the target if the target became obscured.
The angle measured by the graticule also caused a metal wire to rotate around the face of a large circular display on one side of the HACS, known as the ''Deflection Display''. The measured value of altitude and range, and estimated value of target speed, caused optics to focus a lamp onto a ground glass screen behind the wire, displaying an ellipse whose shape changed based on these measures. The deflection operator used two controls to move additional wire indicators so they lay on top of the intersection of the outer edge of the ellipse where it was crossed by the rotating metal wire. The intersection of the ellipse and the target direction was used as a basis for calculating elevation and training of the guns. The ellipse method had the advantage of requiring very little in the way of mechanical computation and essentially modelled target position in real-time with a consequent rapid solution time.
Information flow
![The Royal Navy during the Second World War A3883](https://upload.wikimedia.org/wikipedia/commons/4/4e/The_Royal_Navy_during_the_Second_World_War_A3883.jpg)
The HADT provides target direction, range, speed, altitude and bearing data to the HACP, which transmits direction and fuse timing orders to the guns. The HACP transmits the computer generated range rate and generated bearing back to the HADT, creating a feedback loop between the HADT and HACP, so that the fire control solution generated by the computer becomes more accurate over time if the target maintains a straight line course. The HADT also observes the accuracy of the resulting shell bursts and uses these bursts to correct target speed and direction estimates, creating another feed back loop from the guns to the HADT and thence to the HACP, again increasing the accuracy of the solution, if the target maintains a straight line course. Most guns controlled by the HACS had ''Fuze Setting Pedestals'' or ''Fuze Setting Trays'' where the correct fuze timing was set on a clockwork mechanism within the AA shell warhead, so that the shell would explode in the vicinity of the target aircraft.
Target drones
The HACS was the first Naval AA system to be used against
radio controlled aircraft
A radio-controlled aircraft (often called RC aircraft or RC plane) is a small flying machine that is controlled remotely by an operator on the ground using a hand-held radio transmitter. The transmitter continuously communicates with a receiver ( ...
, and achieved the first AA kill against these targets in 1933. In March 1936, six
Queen Bee
A queen bee is typically an adult, mated female (gyne) that lives in a colony or hive of honey bees. With fully developed reproductive organs, the queen is usually the mother of most, if not all, of the bees in the beehive. Queens are developed ...
targets were destroyed by the RN Mediterranean Fleet during intensive AA practice at a time of extreme tension between the UK and Italy. Target practice against
target drone
A target drone is an unmanned aerial vehicle, generally remote controlled, usually used in the training of anti-aircraft crews.
One of the earliest drones was the British DH.82 Queen Bee, a variant of the Tiger Moth trainer aircraft operationa ...
s was carried out using special shells which were designed to minimize the possibility of destroying expensive targets. The RN allowed media coverage of AA target practice and a 1936
newsreel
A newsreel is a form of short documentary film, containing news stories and items of topical interest, that was prevalent between the 1910s and the mid 1970s. Typically presented in a cinema, newsreels were a source of current affairs, informa ...
has footage of an actual shoot. In 1935 the RN also began to practice HACS controlled shoots of target aircraft at night.
Tachometric and radar additions
![HACS MK IV Table on board HMS Duke of York](https://upload.wikimedia.org/wikipedia/commons/a/ab/HACS_MK_IV_Table_on_board_HMS_Duke_of_York.jpg)
The RN moved quickly to add true tachometric target motion prediction and radar ranging to the HACS by mid 1941. The RN was the first navy to adopt dedicated FC AA radars. However the system, in common with all World War II-era mechanical AA fire control system still had severe limitations as even the highly advanced
United States Navy
The United States Navy (USN) is the maritime service branch of the United States Armed Forces and one of the eight uniformed services of the United States. It is the largest and most powerful navy in the world, with the estimated tonnage ...
(USN)
Mk 37 system in 1944 needed an average of 1,000 rounds of ammunition fired per kill. In 1940 the
Gyro Rate Unit (GRU) was added to the HACS system, an
analogue computer
An analog computer or analogue computer is a type of computer that uses the continuous variation aspect of physical phenomena such as electrical, mechanical, or hydraulic quantities ('' analog signals'') to model the problem being solved. In ...
capable of directly calculating target speed and direction, converting the HACS into a
tachymetric A tachymetric anti-aircraft fire control system generates target position, speed, direction, and rate of target range change, by computing these parameters directly from measured data.
The target's range, height and observed bearing data are fed in ...
system. Also in 1940, radar ranging was added to the HACS. 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. GRU/GRUB could generate target speed and position data at angular rates of up to 6 degrees per second, which was sufficient to track a crossing target at a range of .
The Fuze Keeping Clock
RN destroyers were hampered by the lack of good dual-purpose weapons suitable for ships of
destroyer
In naval terminology, a destroyer is a fast, manoeuvrable, long-endurance warship intended to escort
larger vessels in a fleet, convoy or battle group and defend them against powerful short range attackers. They were originally developed in ...
size; for much of the war 40° was the maximum elevation of the
guns equipping such ships, which were consequently unable to engage directly attacking
dive bomber
A dive bomber is a bomber aircraft that dives directly at its targets in order to provide greater accuracy for the bomb it drops. Diving towards the target simplifies the bomb's trajectory and allows the pilot to keep visual contact througho ...
s, although they could provide "barrage" and "predicted fire" to protect other ships from such attacks. Destroyers did not use HACS, but rather the
Fuze Keeping Clock
The Fuze Keeping Clock (FKC) was a simplified version of the Royal Navy's High Angle Control System analogue fire control computer. It first appeared as the FKC MkII in destroyers of the 1938 ,''Tribal Class Destroyers'', Hodges, p. 27 while late ...
(FKC), a simplified version of HACS. Starting in 1938 all new RN destroyers, from the onwards, were fitted with a FKC and continuous prediction fuse setting trays for each main armament gun. WWII experience from all navies showed that dive bombers could not be engaged successfully by any remote computer-predictive AA system using mechanical fuzes due to the lag time in the computer and the minimum range of optical rangefinders. In common with other contemporary navies, pre-war designed RN destroyers suffered from a lack of short-range, rapid-fire AA with which to engage dive bombers.
The Auto Barrage Unit
The Auto Barrage Unit or ABU, was a specialized gunnery computer and radar ranging system that used
Type 283 radar. It was developed to provide computer prediction and radar anti-aircraft fire control to main and secondary armament guns that did not have inherent anti-aircraft capability. The ABU was designed to allow the guns to be pre-loaded with time fused ammunition, and it then tracked incoming enemy aircraft, aimed the guns continuously to track the aircraft, and then fired the guns automatically when the predicted aircraft position reached the preset fuse range of the previously loaded shells. The ABU was also used with guns that were nominally controlled by the HACS to provide a limited blind fire capability.
Wartime experience
By May 1941, RN cruisers, such as , were engaging the Luftwaffe with stabilized HACS IV systems with GRU/GRUB and
Type 279 radar
The Type 279 radar was a British naval early-warning radar developed during World War II from the Type 79 metric early-warning set. It initially had separate transmitting and receiving antennas that were later combined in the Type 279M to single- ...
with the Precision Ranging Panel, which gave +/- 25 yd accuracy out to 14,000 yds. HMS ''Fiji'' was sunk in the
Battle of Crete
The Battle of Crete (german: Luftlandeschlacht um Kreta, el, Μάχη της Κρήτης), codenamed Operation Mercury (german: Unternehmen Merkur), was a major Axis airborne and amphibious operation during World War II to capture the island ...
after running out of AA ammunition but her HACS IV directed 4-inch AA gun battery fended off Luftwaffe attacks for many hours.
Demonstrating the RN's rapid strides in naval AA gunnery, in May 1941,
HMS ''Prince of Wales'' went to sea with HACS IVGB, with full radar ranging systems, and nine AA associated fire control radars: four
Type 285 radar
The Type 285 radar was a British naval anti-aircraft gunnery radar developed during the Second World War. The prototype was tested at sea aboard the escort destroyer
An escort destroyer with United States Navy hull classification symbol DDE wa ...
, one on each ''High Angle Director Tower'' (HADT) and four
Type 282 radar
Type may refer to:
Science and technology Computing
* Typing, producing text via a keyboard, typewriter, etc.
* Data type, collection of values used for computations.
* File type
* TYPE (DOS command), a command to display contents of a file.
* Ty ...
, one on each
Mk IV director for the
QF 2 pdr (40mm) "pom pom" mounts, and a long range
Type 281 radar
The Type 281 radar was a British naval early-warning radar developed during World War II. It replaced the Type 79 as the Royal Navy's main early-warning radar during the war.
The prototype system was mounted on the light cruiser in October 1 ...
Warning Air (WA) radar which also had precision ranging panels for aerial and surface targets. 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
Operation Halberd was a British naval operation that took place on 27 September 1941, during the Second World War. The British were attempting to deliver a convoy from Gibraltar to Malta. The convoy was escorted by several battleships and an air ...
. Although the shortcomings of HACS are often blamed for the loss of
Force Z
Force Z was a British naval squadron during the Second World War, consisting of the battleship , the battlecruiser and accompanying destroyers. Assembled in 1941, the purpose of the group was to reinforce the British colonial garrisons in the ...
, the scope of the Japanese attack far exceeded anything the HACS had been designed to handle in terms of aircraft numbers and performance. The failure of anti-aircraft gunnery to deter the Japanese bombers was also influenced by unique circumstances. The HACS was originally designed with Atlantic conditions in mind and ''Prince of Wales''s AA FC radars had become unserviceable in the extreme heat and humidity in
Malayan waters and her 2-pdr ammunition had deteriorated badly as well.
The RN made the following claims for ship borne anti-aircraft fire against enemy aircraft, from September 1939 up to 28 March 1941: :Certain kills: 234, Probable kills: 116, Damage claims: 134
The RN made the following claims for ship borne anti-aircraft fire against enemy aircraft, from September 1939 up to 31 Dec 1942:
* Major warships (ships likely to have HACS or FKC fire control systems)
:Certain kills: 524
:Probable kills: 183
:Damage claims: 271
* Minor warships and merchant vessels (most having no AA fire control systems)
:Certain kills: 216
:Probable kills: 83
:Damage claims: 177
:Total kill claims: 740
:Total probable claims: 266
:Total damage claims: 448
Radar and the Mark VI Director
HACS used various director towers that were generally equipped with Type 285 as it became available. This metric wavelength system employed six
yagi antenna Yagi may refer to:
Places
*Yagi, Kyoto, in Japan
*Yagi (Kashihara), in Nara Prefecture, Japan
*Yagi-nishiguchi Station, in Kashihara, Nara, Japan
*Kami-Yagi Station, a JR-West Kabe Line station located in 3-chōme, Yagi, Asaminami-ku, Hiroshima, Hi ...
s that could take ranges of targets, and take accurate readings of bearing using a technique known as "
lobe switching
Lobe switching is a method used on early radar sets to improve tracking accuracy. It uses two slightly separated antenna elements to send the beam slightly to either side of the midline of the antenna. The radar signal switched between the two an ...
" but only crude estimates of altitude. It could not, therefore, "lock on" to aerial targets and 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
Type 275 radar. 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":
* HACS III: ABC transmission, AV cradle for 15 ft 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''*,
''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.
* 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.
: and es.
* 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 15 ft 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.
[Uses FKC AAFC table according to Campbell.]
:HMS ''Indomitable'', ''Implacable'' and ''Indefatigable''.
See also
*
Argo clock
In Greek mythology the ''Argo'' (; in Greek: ) was a ship built with the help of the gods that Jason and the Argonauts sailed from Iolcos to Colchis to retrieve the Golden Fleece. The ship has gone on to be used as a motif in a variety of sour ...
*
Ship gun fire-control system
Ship gun fire-control systems (GFCS) are analogue fire-control systems that were used aboard naval warships prior to modern electronic computerized systems, to control targeting of guns against surface ships, aircraft, and shore targets, with ...
References
External links
Newsreel video of HACS controlled guns in action
More Newsreel footage of HACS guns engaging high level bombers
HACS: A Debacle or Just-in-Time?)Illustration of the HACS Deflection ScreenAppendix one, Classification of Director InstrumentsHACS III Operating manual Part 1HACS III Operating manual Part 2HACS III*G with Type 285 Radar and the MkIII tableBritish Mechanical Gunnery Computers of World War IIProgress in Naval Gunnery, 1914–1936Memoirs of Sub-Lieutenant Robert Hughes, Gunnery Control Officer on HMS Scylla
{{DEFAULTSORT:Hacs
Anti-aircraft artillery
Military computers
Naval artillery
Artillery operation
Royal Navy
Fire-control computers of World War II
Military equipment introduced in the 1930s