History

The Vickers 40mm "Pom-Pom"

QF 2 pounder naval gun

The 2-pounder gun, officially designated the QF 2-pounder and universally known as the pom-pom, was a 1.575 inch British autocannon, used famously as an anti-aircraft gun by the Royal Navy. The name came from the sound that the original models make when firing...

 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. It was, therefore, essential to aim the mount from a remote location, using a 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....

 that had a clear view, free from smoke and vibration. The director crew would aim at the target aircraft and, in the early versions of the director, cause Layer ( Altitude ) and Trainer ( Azimuth ) Pointers to rotate on the gun mount. The gun crew would then move the mount to match the pointers rather than having to try and aim at the target aircraft.

The Pom-Pom Director Mark I - III

Pom-pom Directors I through III controlled the gun mounting through "follow the pointer" control and aimed at aircraft using eye shooting techniques through a simple ring sight. These directors began to appear on Royal Navy Cruisers, Battleships, and Aircraft Carriers in the late 1930s. Most Destroyers and smaller ships that carried Pom-Pom guns continued to rely on aiming the guns with the on-mount gun-sights due to the lack of space on these ships to site a Pom-Pom Director.

The Pom-Pom Director Mark IV

The Mk IV Director was a considerable improvement and used gyroscopes in a Gyro Rate Unit

Gyro Rate Unit

-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-tachymetric anti-aircraft fire control system, that would compute the gun laying orders and the time fuze...

 coupled to an optical 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....

 and Type 282 radar radar to determine the range, speed and direction of enemy aircraft and then used an on-Director computer

Rangekeeper

Rangekeepers were electromechanical fire control computers used primarily during the early part of the 20th century. They were sophisticated analog computers whose development reached its zenith following World War II, specifically the Computer Mk 47 in the Mk 68 Gun Fire Control system. During...

 to produce an accurate fire control solution to hit the target. Later versions of the Mk IV director introduced Remote Power Control

Servomechanism

thumb|right|200px|Industrial servomotorThe grey/green cylinder is the [[Brush |brush-type]] [[DC motor]]. The black section at the bottom contains the [[Epicyclic gearing|planetary]] [[Reduction drive|reduction gear]], and the black object on top of the motor is the optical [[rotary encoder]] for...

 (RPC) and could control the Pom-Pom mounting by remote control from the Director. The Mk IV Director was fully tachymetric

Tachymetric

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....

 but suffered from the fact that the director was not stabilized against the movement of the ship, and consequently required a carefully trained crew to achieve good results. Even so, the Mk IV Director was highly advanced and placed the Royal Navy in the forefront of Naval anti-aircraft fire control

Fire-control system

A fire-control system is a number of components working together, usually a gun data computer, a director, and radar, which is designed to assist a weapon system in hitting its target. It performs the same task as a human gunner firing a weapon, but attempts to do so faster and more...

 when it was introduced to the Royal Navy on HMS King George V

King George V class battleship (1939)

The King George V-class battleships were the most modern British battleships used during World War II. Five ships of this class were built and commissioned: King George V , Prince of Wales , Duke of York , Howe , and Anson .The Washington Naval Treaty of 1922 limiting all of the number,...

 in 1940. Later versions were upgraded with Type 282 radar and RPC beginning in 1941, with HMS Prince of Wales being one of the first ships to receive the radar upgrade, which she first used in action during Operation Halberd

Operation Halberd

-Summary:During World War II, Operation Halberd was a British naval operation in September 1941 to escort a convoy from Gibraltar to Malta....

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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