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3.7" Gun Located
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The 133rd Heavy Anti Aircraft Battery were trained to operate the Q.F 3.7 Inch Mobile Anti Aircraft Gun, Q.F. meaning 'quick firing' and was cable of firing 12 rounds per minute. The 'Mobile' guns enabled the battery to alter their position for the principle element of surprising the enemy as well as to reposition the guns to provide better defence if necessary. These guns had a carriage and limber each towed by a separate vehicle known as a Matador.

Mobile units were generally situated at aerodromes that were considered of greatest operational importance, therefore, they were at high risk of being attacked by the enemy. As Anti Aircraft guns are highly vulnerable in action, full use was to be made of their mobility and capacity to take up alternative positions.

Photos Taylor and
Chaffey collection.

The gun and mounting weighed 9.6 ton and the bore of the gun was approximately 185 inches long with a muzzle velocity of 2600 feet per second. It had a ceiling rate of 32,000 feet and fired a projectile weighing 28lb, the whole shell weighed a total of 50lb and was 38 inches in length.

Les Keelan with shell, Keelan collection.

Learning to operate the guns and instruments in an Anti Aircraft Battery was very complex and would require a great deal of knowledge.The determination of the firing data for an AA gun may be considered as being done in stages. They needed to establish the present location of the aircraft. Then they were required to determine the future position of the aircraft at the time the shell will reach it. After that they must determine in what manner to aim the gun, after allowing for ballistic factors, in order that the shell may reach the aircraft at its predicted future position.

Initially, the plane had to be identified as friendly or foe and this was the role of the Air Sentries better known as 'Spotters'. Any approaching enemy aircraft would be immediately reported to the men on a telescope for positive identification. This position was called Toc/I an abbreviation for Telescope Identification.

Spotters tree. Allen collection
Toc/I, cleaning instrument
Nilsson collection
Once identified as an enemy aircraft the Toc/I would report the bearing and angle of the planes to the Height and Range Finder.The Height Finder could then relay a more accurate height to the instrument known as the Predictor. The GL short for Gun Laying Radar would be also constantly tracking the Enemy Aircraft and providing its information to the Predictor as well.
Height and range Finder,
Chaffey collection
Radar, Howes collection
Predictor, Taylor collection

The predictor was a calculating machine, which could measure movements of the target and calculate a future position.The Predictor was the brain of AA gunnery, one of the operators told me that,
"the predictor could be best described as a mechanical computer, manufactured many years before microchips were invented".

It also provided ballistic data to pass the trajectory through and burst the shell at the future position. All the resultant information from the predictor was transmitted instantaneously and constantly to the dials on the guns.

The probability of shooting down an aircraft with gunfire was very small. A more vital role for AA gunnery was to produce enough fire to cause the enemy aircraft to take evasive action or even abort the bombing run so that the bombing was ineffective in achieving its objective.

The men had to be highly trained to operate the instruments and work quickly and efficiently as a team, as an aircraft will only be in danger for 30-second period. The aircraft must maintain constant height, course and speed while aligning his sights prior to releasing the bombs, this operation is known as the "run up". It is at this stage that the aircraft presented a favourable target to the Anti Aircraft guns of defence and should produce its maximum fire effect as the aircraft is obeying its assumptions.