HAA Air Defence

Britain started the war with a good system of identifying enemy raids which worked well during the duration of the war. In the ‘front line’ was the chain of radar stations and Royal Observer Corps posts. Both these would feed back information on raids back to Fighter Command Headquarters at Bently Priory. The information would be processed then sent back out in the form of air raid warnings to RAF Fighter Groups and the central Gun Operations Rooms of GDA’s who would then issue instructions to the individual gun sites giving permission to engage confirmed hostile raids.

Right How the HAA Air Defence of Britain
worked.

At the start of the war guns were laid on targets by a Predictor and Sound Locator. The Predictor basically estimated how a shell should be fired to hit an enemy aircraft given a known height (given by a height finder instrument) and a given wind velocity – i.e. it ‘predicts’ where the aircraft will be by the time the shell reaches it. An electric cable connected the Predictor to the gun and by means of indicators gave the gunlayer his aiming directions. The Predictor could only work if the enemy aircraft could be seen. In cases where it could not (e.g. if flying above low level cloud) a Sound Locator would be needed. By training the Locator towards the approach of enemy aircraft the height and direction could be determined and the gun laid by making allowance for the time it takes the sound of the aircraft to reach the Locator. A system of barrage fire, known as the “Fixed Azimuth” system, had been worked out prior to the war, but relying on sound for its information was inaccurate.

 Top Left: AA Predictor. Top Right: How the predictor works
 Bottom Left: Sound Locator. Bottom Right: Artists impression of a HAA Command Post early in the war. On the left the spotter is looking
 into his special telescope. On the right is the Gun Position Officer who is following the course of hostile aircraft through his field glasses
 and in the centre the Sergeant gives orders to the guns by signal and through a megaphone.

During 1940 Gun Laying Radar was in the process of being developed. At first the performance of radar was varied due to the pattern of obstructions surrounding the site. This was solved by the end of 1940 by the development of Gun-laying (GL) mats (a cat’s cradle of strained wires supporting 2” netting which surrounded the radar with a known uniform area of electrical properties). Gun-laying radar and mats were installed at Suffolk’s static batteries. However these GL stations occasionally caused interference – Nore Command informed 6 AA Brigade that the station at H7 (Old Felixstowe) would have to move owing to interference. It was suggested to move the GL station to H2 (Trimley) and H7 would become a satellite to H1 (Landguard).

The enemy could avoid all these systems either by changing height or direction. However this would make bomb laying harder as this required an even level flight. If the guns could prevent the enemy from accurately bombing the target they would have achieved their purpose. An intelligence report of 2 AA Div noted that the most common evasive tactic of enemy bombers was the execution of gentle ‘S’ turns coupled with a loss of height. However many captured enemy airmen maintained the best policy was to fly straight through if caught in a heavy barrage as they would be through it more quickly. If things became too uncomfortable, a steep dive was the most effective form of evasive action. It is interesting to note that on one raid on the night of 29th/30th Sept 1941, enemy bombers engaged by H2 at Lowestoft took evasive action and prevented H1 from obtaining a satisfactory predicted point.

Low level attacks (often referred to as ‘hedge hopping’ ) were also hard to pick up. Even gliding towards the target was used to try and avoid detection – raiders were suspected of using this tactic on Feb 21st 1941: at 1138 hrs enemy aircraft entered 2 AA Div area at Mendlesham then headed to Lowestoft via Kessingland at 1206 hrs when plots of the raid were lost. About three minutes later unidentified aircraft dropped 10 HE bombs on Lowestoft. As the raid was not heard approaching it was considered a gliding attack at about 4,000 feet was made.

Many engagements were against ‘Unseen’ targets. Unseen targets were subject to a number of restrictions and could only be engaged when:

  • Adverse weather conditions or the unserviceability of aerodromes did not allow fighters to operate.
  • The Air Raid Warning Red was received (although the Harwich guns could open fire seawards on unseen targets without this restriction).
  • There was no friendly aircraft over or approaching the gun zone.
    • Both the Harwich and Yarmouth GDA’s would require special permission to engage unseen targets (this compared to other areas e.g. Coventry, London area, Bristol and Plymouth, which could open fire without prior permission unless an order prohibiting fire had been received).

      In certain circumstances HAA guns and fighters would operate together at night if the enemy were attacking in force over a certain area. This would require weather conditions and visibility to be suitable for night fighters to operate. The code word for this type of operation was “FIGHTERNIGHT”. However AA Command disliked these "Fighter Nights", and would have preferred a system of seperate zones for fighters and guns. This was achieved to some extent in 1942 with the introduction of Indicator belts, Killer belts and GDA layout for searchlights where fighters more or less operated in the Killer and Indicator belts only.

      FIGHTERNIGHT would operate over a radius of 10 miles over the town on which it had been ordered for and the area would be known as a FIGHTERNIGHT restricted area. Searchlights could be used to provide marker zones. In case of FIGHTERNIGHT being ordered HAA sites would be notified of a maximum height to which gunfire was to be restricted.

      A particular raid in July 1941 illustrates the above cooperation between fighters and HAA guns: At 2345 hrs Yarmouth and Lowestoft gun sites were given permission to engage all hostile raids without further reference. At 005 hrs FIGHTERNIGHT was ordered with height restriction of 12,000 ft reduced to 6,000 ft at 0125. At 0017 hrs the permission to engage all hostile raids without further reference was withdrawn although at 0024 hrs permission was given to engage any raid that could be confirmed as hostile.

      However the guns were certainly at times hindered by the presence of friendly aircraft: “Engagements in the Yarmouth and Lowestoft areas were handicapped by the number of friendly aircraft flying in the G.D.A., both bombers and fighters. At one period no less than 8 friendly fighters were plotted within a radius of 40 mls of the G.D.A and the plots on these were both few and unreliable” – 2nd AA Div Intelligence report No 350 on activity during Sept 29/30 1941.

      If invasion was imminent, by 1941 AA Command had arrangements in place to reinforce certain Vulnerable Areas and Points. The code word for this was “ATTIC”. The day on which “ATTIC” was issued would be regarded as D1.

      Guns would move by rail or road. For road moves, guns were to be emplaced and ready to fire at 1200 hrs on D26. Guns would be withdrawn from other Vulnerable Areas to reinforce the Areas under “ATTIC”. Sites for the re-deployed guns had already been recced. Harwich was one of the Vulnerable Areas to be reinforced with 16 3.7” mobiles to be deployed at sites H2 and H4. The guns would be taken from the Vulnerable Area Tyne and Blythe. Harwich was also to be reinforced with four light anti-aircraft guns (to be taken from Chelmsford).

      Concealment of the re-deployment of the guns was to be of paramount importance. Tents etc were not to be erected if they could not be concealed and there was a danger of disclosing the gun position. The re-deployment sites had already been recced.

      Finally it is of interest to note one of the most intensive engagements that AA units in Suffolk were involved in which occurred on 5th March 1942. Enemy aircraft entered the Yarmouth GDA at approx 1402 hrs and there was then an almost constant engagement by both LAA and HAA units until 1612 hrs. The reason for the raid was uncertain but it was considered that enemy raiders were looking for a shipping convoy but finding no targets apparently crossed the coast individually looking to attack Lowestoft and Yarmouth. What was unusual though was that only three of the 11 raids actually dropped bombs. The raiders approached at heights from 800 ft to 4,000 ft and it was thought that the volume of AA fire both from LAA and HAA guns was such that it prevented them from approaching the target. In all the HAA guns fired 473 rounds of 3.7” HE and 50 rounds shrapnel and 58 rounds 3” HE and 18 rounds shrapnel. One enemy aircraft was confirmed destroyed and another almost certainly destroyed and four others hit and damaged. The reason for the success of this engagement was considered to be the unrestricted fire policy allowed to the guns, no friendly aircraft in the area and the heights at which the raiders approached allowing both LAA and HAA guns to engage them.

      References:
      Britain’s Wonderful Fighting Forces, Oldhams Press Ltd
      Roof Over Britain, HMSO, 1943
      AA Command, C Dobinson, Methuen, 2001
      6AA Div papers, TNA
      2 AA Div papers, TNA
      99 HAA Regt papers, TNA

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