Guided Weapon System 2.

The following notes are taken from the GWS2 handbook.

The Guided Weapon System Mk2 (GWS2) forms part of the Action Data Automation Weapon System Mk1 ((ADAWS1) fitted in HM Ships Glamorgan, Fife, Norfolk and Antrim. GWS2 is essentially a beam riding system which uses the same principles as used in GWS1 but includes the following main improvements:
a) The facilities provided by ADA are used for solving missile direction and other problems.
b) Low flying and surface targets can be engaged.
c) Target range, missile range and target height can be measured.
d) Stabilisation can be improved.

In common with other users, GWS2 employs the services of the Data Processing System DAB (ADA), a digital computer system. The main source of information automatically fed into ADA are:
a) Radar Type 965P -range and bearing (early warning).
b) Radar Type 992P -range and bearing.
c) Radar Type 278M -angle of sight [elevation].
d) Radar Type 944M -identification.
e) Stabilisation System Mk2 -pitch,roll and course angle.
f) Ship's Inertial Navigation System.
g) Digital Plot Transmission (DPT).
h) Tactical Information Data Exchange (TIDE).
[Items g and h are target information from other ships.]

ADA uses the information listed above to carry out the following processes:
a) Automatic detection and tracking by surveillance radars.
b) Classification of targets into categories.
c) Threat evaluation.
d) Weapon allocation.
e) Production and transmission of target information.
f) Selection of search patterns.
g) Selection of mode of engagement, salvo size etc.
h) Computation of time to fire.

The information derived from this processing can be visually presented on the display consoles located in the operations room. These consoles also provide facilities for the injection of additional information into ADA.
The two main consoles are:
Command Console.
The command console has the normal ADA displays and facilities which enable the Command to approve, veto or question recommendations from ADA.

Missile Director Officer's Console.
The MDO's console has, in addition to the normal ADA displays and facilities, an end-of-engagement display, a blind-arc display, and a control panel. These extra items show the state of the GWS2 and enable the missile controller to start the firing sequence to engage a target selected by DA. The missile controller can also stop the firing sequence, destroy missiles in flight, re-acquire or re-engage a target.

The main functions of the Type 901M radar are as follows:
a) To acquire air and surface targets at a range to allow a maximum range engagement.
b) To track the target automatically in three co-ordinates.
c) To transmit signals so that a missile is gathered after launch and then guided to intercept the target.
d) To measure target, beacon, and missile ranges so that the instant of initiation of commands to the missile can be computed and the commands transmitted at the correct moment.
e) To provide a suitable angle of sight programme when engaging surface targets.

The Type 901M transmits three conically-scanned beams as follows:
a) Tracking -a pencil beam.
b) Gathering -a wide-angle beam which has its own aerial system. This beam enables the missile to direct itself into the narrow guiding beam soon after launching.
c) Guiding -a pencil beam coaxial with the tracking beam. After the missile is gathered, this beam directs the missile to the target.

TSO's cabinet. The TSO's cabinet enables the TS officer to assist the missile controller to control a normal engagement and, in an emergency, to conduct an engagement.

Display cabinet. The display cabinet contains the Type 901M displays and controls to enable the following actions to be taken:
a) The aimer and target ranger to manually acquire the target indicated by ADA.
b) The missile ranger to supervise the auto-acquisition of the missile or beacon echo and, in the event of a failure, to acquire manually.
c) The aimer to obtain a measure of target height from a television display when engaging low-flying targets.

Director. The GW Director Mark 1 Mod 1 is unmanned and comprises a stabilised platform upon which the radar Type 901M aerials and a television camera are mounted: movements of the aerials are thus made in the true horizontal and lateral planes, ie bearing and angle of sight.

Firing is initiated by the missile controller (or the TSO pressing the...push and, during a single-shot firing from either barrel; this action...the appropriate FSU which, after the firing sequence has been completed (about...seconds), launches the missile. During salvo firing, the left missile is launched first as described previously and, at a predetermined time after the left missile leaves the launcher, the right FSU launches the right missile of the salvo.
[Original document unclear]

Structurally the Mark 2 missile is cylindrical with a tapered nose and has four fixed wings fitted near the centre. Four aero-dynamic control surfaces (fins) at the tail of the missile can be deflected to roll-stabilise the missile and direct it along the radar beam.

The rapid acceleration required for launching and for attaining flight velocity is provided by four solid-fuel boost motors. The boost outlet nozzles are angled so that the missile is made to rotate, thus reducing any dispersion tendency during the boost phase. At the end of the boost phase, the motors are released and fall into the sea. The powered flight of the missile is maintained by the sustainer motor which is automatically fire when the boosts separate from the missile.

Roll Stabilisation. The missile gyro provides a stabilised reference; signals from this gyro move the fins to bring the missile to its correct flight attitude at the end of the boost phase and maintain this roll stabilisation throughout the remainder of the flight.

Gathering. After the missile is roll stabilised, it is probably displaced from the centre of the guiding beam and needs to be "gathered". From signals transmitted in the conically scanned gathering beam, he guidance receiver in the missile senses its position in the conical scan and produces error signals proportional to the distance and direction that it is away from the electrical centre [Datum line] of the guiding beam. These signals initiate movement of the missile fins to bring the missile into the guiding beam.

Guiding. About eight seconds after boost separation, the guidance receiver is switched to respond to signals in the guiding beam. These signals enable the missile to sense its position relative to the beam and the missile control system constantly corrects the course of the missile to maintain its position in the guiding beam.

Interception. At interception the missile uses an infra-red fuze to detonate the warhead; if the target is classed as 'cold' then the warhead can be detonated by command from the ship.


Relax. During the "relax" period, the GWS2 is in the one-minute state of preparedness, surveillance radars are in use but the Type 901M is not radiating. The system is switched to TSO Control and stand-by settings of bearing, angle of sight, and range are applied. Missiles are in the loader but are not supplied with warm-up current and cooling air until ordered.

Stand To. At "stand to" the radar Type 901M is brought to instant readiness, the system is switched to MDO control and the launcher is loaded.

Modes of engagement. The following modes of engagement can be used by GWS2:
a) Line of sight beam riding [LOSBR]
b) Constant angle of sight [with terminal dive -CASWTD]
c) Midcourse constant angle of sight with beam riding (Micawber).
d) Up and over trajectory.

The missile controller checks the following points:
a) That the "901 ready" and "barrel ready" lamps are burning.
b) That the director, launcher and TI are in line and in clear arcs (blind-arc display).
c) That there are no friendly ships or aircraft in the line of fire (marker display).

When the target marker nears the square firing point marker on the marker display, the missile controller presses the "about to fire" push to warn the ship's company and, when the target marker comes within the firing point marker, presses the fire push to start the firing sequence.

The operation of the fire push starts the operation of the left firing sequence unit. This burns the "Fire" lamps on the MDOs console and the TSO's cabinet, sends a signal to ADA and initiates, in the left missile, the firing of the gas generator, uncages the gyro, starts the fuze cooling and clamps the phase shifting motor. The resulting pressure from the gas generator drives the hydraulic pump and the turbo generator to produce hydraulic and electrical power within the missile. A signal is applied to the missile in the left hand barrel to ensure that the decoding circuits are switched to respond to the arm-first command (all missiles are supplied preset to respond to the arm-first command).

At the same time that the signal to uncage the gyro is sent, the phasing error (beam) computer in the phasing reference cabinet is started. The signal proportional to the radar reference correction (Φb) is added to the other phase correction already being applied to the right missile (the phase-shifting motor in the left missile is clamped). The Φb signal is also applied continuously to the radar Type 901M reference thus both the transmitted reference and the right-missile reference are kept in phase with the left missile reference.

The next event to occur in the firing sequence of the left missile is the change over to the missile's electrical load from the ship's 2.4 kc/s supply to the missile generator. The remaining firing control circuits to the left missile are then opened and the LEAP is retracted and housed.

The closing of the LEAP door completes the firing circuits to the boost motors of the left missile. The boost motors fire and the missile accelerates out of the launcher.

If a salvo is ordered, the launching of the left missile initiates the action of the salvo timing unit which, after a predetermined salvo interval starts the right FSU. The sequence for firing the right missile then proceeds as described above with the addition that, about one second after the gas generator has fired, the firing circuits of the right missile are switched automatically to receive the arm-second command, and the operation of the beacon transponder is inhibited.

When the missile is launched, the missile and beacon radio servos in the TS annex run to a preset range and wait for the missile range and beacon range signals to appear.

Boost period. Under the thrust of the four boost motors, the missile accelerates and rotates about its longitudinal axis. During this period, the guidance equipment is inoperative and the fins are locked at 20' anti-roll. This offset has the effect of reducing the roll rate towards the end of the boost phase. After about 3 seconds flight, the thrust from the boost motors decays and the spent boosts, together with their attachments, are discarded leaving the missile to fly unencumbered.

The mechanical action of boost separation fires the sustainer motor of the missile, starts the time and range unit, and energises the missile beacon transponder. The sustainer motor maintains the speed of the missile and the efflux from the motor unlocks the fin clamps which are swept away.

Roll Stabilisation. The first switching action of the time and range unit puts the missile under the control of the roll gyro. The resulting movements of the control surfaces stop the missile rolling and the bring the missile to its correct flight attitude within one second of boost separation. This roll stabilisation is then continued throughout the whole of the missile's flight.

Gathering. At a pre-determined time after boost separation, the missile guidance equipment is switched into operation and the pulse pattern in the wide gathering beam of the Type 901M is received in the guidance equipment. From these signals the displacement of the missile from the electrical centre of the gathering beam conical scan is computed by the guidance receiver and correcting signals are converted to mechanical movement and hydraulic actuators move the control surfaces to direct the missile to the electrical centre of the gathering beam conical scan which is coincident with the centre of the guiding beam [except for small angles of sight].
[For angles of sight from 7.5 degrees down to 0·5° the gathering beam remains at 7·5° to avoid the effects of sea reflections.]

Guiding. At a pre-determined time after boost separation, the guidance receiver is switched to respond to the guiding transmissions from the radar Type 901M. The missile is controlled as described above for gathering, and now rides the [narrower] guiding beam to the target.

Arming the warhead initiator. The warhead initiator is armed after the following events have occurred.
a) The missile has sustained a high forward acceleration [13g] for two seconds.
b) A further six seconds has elapsed.
c) Boost separation has taken place.

Missile range. When the missile and beacon range signals are detected, an opening range rate is applied to the missile and beacon ranging servos. After a period of sustained detection, each servo is switched to AUTO and follows the appropriate signal.

Range difference. The range difference servo, which is already fed with target range, is now supplied with the beacon range. The resulting range difference and range difference rate are used to compute the correct moment to initiate some of the commands to be sent to the missiles during flight.

Arming the fuze. The arm commands are initiated by the fuze arm computer in the phasing reference cabinet in the TS annex. Separate signals are transmitted on both the gathering and guiding beams, and lamp indication that arm commands have been initiated, is given on both the MDO's console and the TSO's cabinet.

The initiation of the "arm" commands is based upon range difference and range difference rate and is sent about four seconds before interception.

Half a second before interception by the first missile of a salvo, the auto-follow constant of the target ranging servo is changed for two seconds after which period the servo reverts to normal operation. This action prevents the radar losing lock on the detonation of the first warhead.

Detonation. Once it is armed, the infra-red fuze in the missile will normally detonate the warhead when it intercepts the target. If, however, the target is classified by ADA as one which it is unlikely to actuate the infra-red fuze the warhead is exploded by a command initiated by the range coincidence detector in the missile range cabinet.

Resetting. When the missile controller sees from his display that the target is destroyed or both missiles should have passed the intercept position and the re-engagement lamp is not burning, he presses the reset push. This causes the computers to be reset and the director control and target range servos to run to the TI (or standby) settings This prepares the GWS2 for another engagement.

Surface Targets. When engaging surface targets in the constant angle of sight [CASWTD] mode, the procedure is similar to that for low fling targets with the following differences:
a) ADA does not select surface targets consequently it has to be "informed" of a surace engagement by the Command using manual injection.
b) The television system is not required because the dive computer uses zero height.
c) The missile fuze is not armed.

MICAWBER. If a closing target is flying between 500 and 800 feet at the moment of firing, it will be above the sea reflection zone (θ°) at normal interception range. In this instance, although the engagement is started in the constant angle of sight mode, the system will automatically change to the line of sight mode beam riding when the angle of sight rises above θ°. This mode of firing is known as Midcourse Constant Angle of sight With Beam Riding (MICAWBER). It the target dives below 500 feet after the mode has changed, line of sight beam riding is continued.

Up and Over Trajectory. The up and over trajectory mode of engagement is used against surface targets at long range. In this mode, the angle of sight of the radar Type 901M is made to follow a programme dependent upon range difference. The dive computer is not used but when the angle of sight reaches θ°, a command signal causes the missile to glide, ie to ignore the radar reference signals, which may be affected by sea reflections, and to keep the same path to interception.

Because of the programmed angle of sight movement, radar Type 901M cannot acquire the target but is kept aligned with the target by following training transmissions from radar Type 903 (MRS3). When the up and over trajectory mode of engagement is selected by ADA and approved by Command, target information is fed from ADA to radars Type 901M and type 903.

The target is acquired by the MRS3 in the normal way and radar type 901M follows transmissions from the radar Type 903 for range and bearing. The engagement then proceeds normally except that the missile glides to the target (as described above), and that the arm command is not sent. Only single shot mode can be used in the up and over trajectory type of engagement.

Availability. The availability requirements of the GWS2 are as follows:
a) To operate at the designed performance for four hours.
b) To remain at immediate notice for four hours.
c) To remain at reduced notice for 14 days.:

Types of missile. The following types of missile are carried:
a) Operational, briefly described above and painted white with a black stripe from nose to tail to indicate the top-in-launch position. A red line around the warhead indicates it is filled with explosive. Red crosses painted around the boost and sustainer motors indicate that they are filled with propellant. [The propellant markings were later changed to brown bands, a line with red crosses was used to indicate the presence of hazardous materials in the fuze].
Practice, fitted with a telemetry section in place of a warhead. The telemetry section is painted salmon pink; the remainder of the missile is painted as described above for an operational missile. [In my experience these missiles were always called Telemetry missiles.]
Service and training, fitted with inert sustainer and boost motors. The missile is painted black and has FREE FROM EXPLOSIVE and INERT FILLED painted in white on both sides of the sustainer motor. The boost motors are painted white with the words DUMMY MOTOR in blue. [Later there was a differentiation between DRILL and DISPLAY missiles. The former were the same weight as an operational missile but did not necessarily look like an operational missile; they were often made of modified Mk1 components and painted a dark (Oxford) Blue. The latter were visually identical to an operational missile but had no ballast weights and so were lighter; they were painted red. A further version was both visually identical to an operational missile and the correct weight, these were known as DRILL/DISPLAY missiles.]

Acquisition. ADA provides TI signals for an approved target to operate the following servos.
a) Director control servo (bearing).
b) Director control servo (angle of sight).
c) Target range servo.

These servos, in turn, control the movement of the director and set up the target ranging system. TI signals are available throughout an engagement making it possible to revert to TI for re-acquisition if aim in auto-follow is lost (although missiles in the beam will be lost in doing so) or to provide range for the fuze arming computer if radar Type 901M range is lost.

Searching. Since the target information from ADA or from other sources is unlikely to be sufficiently accurate to ensure that the narrow tracking beam is pointed directly at the target at the start of acquisition, it is necessary for radar Type 901M to search about the indicated position of the target.

Selection of search patterns. ADA selects and starts the search pattern appropriate to the expected accuracy of the source of information upon which the target information fed to the Type 901M radar is based. The type of search and the end of each pattern is indicated on the display cabinet in the TS. The search continues until the target is acquired or the system is reset.

If, during searching, the source of target information is changed, the search pattern is changed automatically. If an X search is in progress the change is made immediately, otherwise the change awaits the end of a pattern. If necessary, the search can be enlarged by pressing a push on the TSO's cabinet.

Search patterns. The type of search pattern is designated by quoting the number of degrees of bearing and angle of sight covered by the pattern. All patterns are superimposed on TI (or standby) bearing and angle of sight and include the normal conical scan. The basic search pattern is produced by movement of the BAU, larger patterns are made by moving the director in addition to the BAU.

The various search patterns are described below together with the circumstances in which they are used.
a) Pattern 2.2. The basic pattern traced out by BAU movement; it takes one second to complete. It consists of a circular scan with a radial beam displacement of 45 minutes of arc covering a volume with a conical angle of 2°. This pattern is used when bearing is obtained from radar Type 992P and angle of sight from radar 278M under good conditions.
b) Pattern 2.4. This pattern (illustrated by diagram 4.1) is made by the BAU basic pattern with additional sinusoidal angle of sight movement of the director. It takes 3 seconds to complete and covers 2° of bearing and 4° of angle of sight. It is used when bearing is obtained from radar Type 992P and angle of sight from radar Type 278M.
c)Pattern 2.6. Formed in much the same way as pattern 2.4, but 6° of angle of sight are covered in 5 seconds. This pattern is used when bearing is obtained from radar Type 992P and angle of sight is based upon the TIDE link and range from local radar.
d)Pattern 2.X. This consists of the basic pattern combined with a downward sweep of the director. The maximum angle of sight is determined by ADA. The time taken for each pattern varies with the maximum angle of sight, but a 50° sweep takes 38 seconds. This pattern is used when bearing is obtained from radar Type 992P but only approximate and range information is available from TIDE.
e) Pattern 4.2. As for pattern 2.4 but with the director moving sinusoidally in bearing. It is used when the bearing is obtained from radar type 965P and angle of sight from radar Type 278M under good conditions.
f) Pattern 4.4. This pattern (illustrated) is produced by the basic pattern and simultaneous sinusoidal motions applied to director bearing and angle of sight to complete a pattern in 5·5 seconds. It is used when bearing is obtained from radar Type 965P and angle of sight from radar Type 278M.
g) Pattern 4.6. For this pattern the director moves sinusoidally in angle of sight and makes a step in bearing at the peak of each angle of sight sweep. The pattern, which takes 5 seconds to complete, is used when bearing is obtained from radar Type 965P and angle of sight from TIDE.
h) Pattern 4.X. The director moves sinusoidally in bearing and sweeps downward in angle of sight. The maximum angle of sight is determined ADA. The time taken for each pattern varies with the maximum angle of sight but a 50° sweep takes 75 seconds. This pattern is used when bearing is taken from radar Type 965P but only approximate height and range information is available.

Emergency search patterns.
The following search patterns are selected by positioning the emergency switch on the TSO's cabinet when emergency control is in use.
a) For AA engagements the search comprises two 4.X patterns side by side, the maximum angle of sight being set by the angle of sight handwheel on the TSO's cabinet.
b) For surface engagements the 4.2 search pattern is used, the search being made around 1° angle of sight set by the TSO's handwheel.

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Last updated: 9thJune 2020.
Copyright SR Jenkins, March 2019.