Gyro Rate Unit
Encyclopedia
History
The Royal Navy, after World War I, became increasingly concerned with the threat posed by aerial attack. In 1930 the RN began equipping ships with the High Angle Control System, a non-tachymetricTachymetric
A tachymetric anti-aircraft fire control system refers to a method of generating target position, speed, direction, and rate of target range change, by computing these parameters directly from measured data....
anti-aircraft fire control system, that would compute the gun laying orders and the time fuze setting of the anti-aircraft guns, to hit the target. The HACS marks I through IV depended upon the control officer inputting to the computer an estimated aircraft direction, and speed, which was combined with range and height measurement from an optical coincidence rangefinder
Coincidence rangefinder
A coincidence rangefinder is a type of rangefinder that uses mechanical and optical principles to allow an operator to determine the distance to a visible object....
to permit the computer to form a solution. The control officer would estimate target speed based upon aircraft type, while target direction could only be crudely measured by aligning the graticule of his binoculars
Binoculars
Binoculars, field glasses or binocular telescopes are a pair of identical or mirror-symmetrical telescopes mounted side-by-side and aligned to point accurately in the same direction, allowing the viewer to use both eyes when viewing distant objects...
with the aircraft fuselage. Unfortunately, these estimates of target speed and direction were often in error, and it took time for the HACS to correct these estimates through a feedback loop from the director
Director (military)
A director, also called an auxiliary predictor, is a mechanical or electronic computer that continuously calculates trigonometric firing solutions for use against a moving target, and transmits targeting data to direct the weapon firing crew....
to the computer, thus delaying the generation of a correct fire control
Fire control
control of fire 'control of fire' is the practice of reducing the heat output of a fire, or reducing the area over which the fire exists, or suppressing or extinguishing the fire by depriving a fire of fuel, oxygen or heat ....
solution and reducing the accuracy of the resulting gunfire. In the late 1930s the Royal Navy began to investigate the possibility of combining gyroscopes with optical sights to directly and accurately measure target aircraft speed and direction.
The Gyro Rate Unit
A gyroscope was attached, via mechanical linkage, to an optical monocularMonocular
A monocular is a modified refracting telescope used to magnify the images of distant objects by passing light through a series of lenses and sometimes prisms; the use of prisms results in a lightweight telescope. Volume and weight are less than half those of binoculars of similar optical...
sight to form the Gyro Rate Unit or GRU. Gyroscopes, when spinning, will resist movement while seeking to remain vertical. As the cross-hairs of the optical sight are kept centred on the moving aircraft the mechanical linkage will pull the gyroscope in the direction of the aircraft movement. The force required to move the gyroscope is proportional to the observed target movement across the line of sight. This force was measured by the deflection of a spring-loaded device and the deflection measurement was combined with rangefinder, and/or, radar measured target range and altitude in a specialized computer, the Gyro Rate Unit Box ( GRUB ).
The Gyro Rate Unit Box
The Gyro Rate Unit Box used the measured target motion, range and height, to accurately determine the true direction of movement of the target, including its rate of altitude change, and passed this information to the HACS computer, which then generated the gun laying orders and the correct time fuze setting. The HACS computer could not directly use rate of altitude change information, so the GRUB would calculate the target altitude, direction and apparent speed for a short interval of time, equal to the loading cycle of the guns, in advance of the actual time and feed this to the HACS computer allowing it to generate correct gunlaying and fuze setting orders. The GRUB thus converted the HACS into a tachymetricTachymetric
A tachymetric anti-aircraft fire control system refers to a method of generating target position, speed, direction, and rate of target range change, by computing these parameters directly from measured data....
fire control system. The GRU and the GRUB began to appear on RN ships in 1940. The GRU/GRUB could calculate target speed and direction for targets with a maximum speed of 360 knots, or 6 degrees of target motion per second and was most accurate at shorter ranges where apparent target motion was highest. GRU/GRUB was also used on The Pom-Pom Director
Pom-Pom Director
-History:The Vickers 40mm "Pom-Pom" Antiaircraft mounting was introduced to the Royal Navy in the early 1930s. The mounting was capable of a tremendous volume of fire but the crew had great difficulty in aiming the mounting due to the smoke and vibration created by the guns...
, Mark IV, and with the Fuze Keeping Clock
Fuze Keeping Clock
The Fuze Keeping Clock was a simplified version of the Royal Navy's High Angle Control System analogue fire control computer. It first appeared as the FKC Mk1 in destroyers of the 1938 Tribal class, while later variants were used on sloops, frigates, destroyers, aircraft carriers and several...
.
External links
- The Pom-Pom Director, Mark IV in The Gunnery Pocket Book, B.R. 224/45, 1945 placed online courtesy of Historic Naval Ships Association
- Illustration of the Pom-Pom Director, Mark IV in The Gunnery Pocket Book, B.R. 224/45, 1945 placed online courtesy of Historic Naval Ships Association
- BRITISH MECHANICAL GUNNERY COMPUTERS OF WORLD WAR II
