The type of low level air attack expected against Vulnerable Points or military targets was:
Dive bombing attack, whether starting from high or low altitude
Low level flying attack with machine guns
Low-level bombing attack
Gas spray attack
To provide all round protection, the principle of LAA defence was to site guns near the Vulnerable Point. To guns so sited, the enemy aircraft would fly straight down the trajectory, facilitating engagement. Guns were normally sited singularly but sufficiently close together to enable a high volume of fire to be brought against low flying aircraft.
At the outbreak of War, LAA guns were few and far between although each Chain Home Station had been provided with three Bofors. By 1940 Naval Ports had received LAA guns for protection (as well as HAA guns). It was recognized that any German invasion would need to obtain a high degree of air superiority if it was to be successful. Hence it was expected that the preliminary enemy action to invasion would include the sever bombing of forward aerodromes, either to put them out of action or to knock out defences with the aim of seizing them with glider or parachute troops in order to land further airborne forces. As a result forward aerodromes were provided with both HAA and LAA guns for protection.
Shortages in modern LAA guns resulted in a variety of weapons being used in this role which as well as the new Bofors included the Lewis and Bren light machine guns, Hispano Suiza 20mm guns and Oerlikon 20mm guns. As more Bofors became available, this allowed some of the lighter weapons to be replaced. For example, during 1940 Martlesham aerodrome was defended by four Bofors and 10 Lewis guns. During October 1941, four more Bofors arrived, leading to the displacement of two sets of quadruple mounted Lewis guns (four retained by the new Bofors detachments for close defence and four sent to a Search Light Battery). However the demands of training and operational requirements meant there was always to some extent a shortage of guns. Two Bofors had to be temporarily withdrawn from Martlesham to Trimley during October 1941, for the use of 307 LAA Battery for training.
Above: Left - Lewis Gun mounted for AA role. Middle - quadruple mounted Lewis guns.
Right - 20 mm Hispano Suiza, Mildenhall Aerodrome (note pillbox in background).
Light AA guns were instructed not to open fire at extreme range, but rather were to follow targets at long range and hold fire until targets reached an effective range. The following Ground Range and Height were given as a guide for effective range:
Each gun was allocated a ‘priority arc’ which was to be marked in gun pits. Guns would engage any target within range if no target was in their ‘priority arc’. A fighter attacking would take precedence over AA gun fire. If a fighter signaled a succession of dots on its downward recognition light, it would mean it was about to attack and AA gun fire would cease.
In certain circumstances, light anti-aircraft gun defences were considerably strengthened by the addition of aerial obstacles, i.e. a balloon barrage.
During the second half of 1941, the enemy made a number of fleeting attacks over certain coastal towns on the South and East Coasts – so called “Fringe Targets”. Unlike the majority of the previous battles fought by AA Command, the Battle of the Fringe Targets, or as it was more popularly known as “Tip and run raids”, was an almost entirely LAA affair. In East Anglia, Lowestoft and Great Yarmouth suffered heavily in these raids. The provision of LAA guns was very problematic in that there were just not enough guns to cover all approach routes of enemy raiders. General Sir Frederick Pile summed up the Battle of the Fringe Targets as follows: “The supply of equipment was never sufficient for success until a great damage had been done. The fact that the British always win the last battle, and pride themselves on the fact – as if in some way it were more credible than winning and decisively at the first encounter and saving a lot of lives, time, trouble and expense – was largely the outcome of this supply problem. We couldn’t win the first battle because we were never ready, so we made a virtue out of necessity and drew what comfort we could from the cliché”.
Deployment of LAA guns for Ipswich began in May 1942 when 100 LAA Regt arrived with eight 40mm Bofors. The communication of information to the LAA sites was by dispatch riders form HAA sites H12 (Nacton Heath) and H19 (Stores Parr). Lowestoft had twelve 40 mm Bofors deployed for defence in April 1942. The Bofors usually operated as a team with one search light – these searchlights were referred to as “Canopy” searchlights.
On Oct 2nd 1942, notification was received that four 40mm Bofors were to be deployed for the protection of Felixstowe Town and Southwold. A further four guns were promised for Felixstowe in the near future. Guns were seldom located at a site for more than a few months and in some cases acted as a “circus”, for example four additional Bofors were allocated to Ipswich during the full moon period from 19th to 25th November 1942.
The siting of guns was not straight forward. If sited on high ground, sufficient depression may not be obtained to engage low flying raiders. If sited on low ground, the amount of dead ground could be enormous. An illustration of this problem, actually caused by anti-invasion defences, was raised on October 24th 1942, when Bofors deployed at Felixstowe could not fire below 8˚due to steel scaffolding on the beach. As the G.O.C 54th Division was unwilling to remove the scaffolding a request was made to construct a platform to lift the gun eight foot above the ground.
During October 1942 LAA guns were given permission to engage all aircraft, except flying boats and four engine bombers or a fighter with lowered undercarriage as a sign of distress, approaching seaward at below 500 ft without prior recognition, between first and last light daily. This was as a result of the need to protect British fighters, as the question of identification was not always straight forward between a fast flying friend and foe. The high state of readiness would also mean gunners were quick to open fire. Eventually it was decided that no British fighter would approach the coast at less than 1,000 feet - gunners were told 500 feet to allow for bad estimates! Any fighter below that height was to be automatically engaged.
Mobile LAA guns would have had a simple sandbagged or earthwork emplacements built around them. A standard design was often used for Bofors. Static Bofors, deployed for more permanent protection at certain Vulnerable Points, were mounted on concrete set holdfasts or cruciform baulk platforms. Bofors used for protection of coastal towns seldom stayed on the same site for more than a few months – the shortage of guns meant they were constantly being moved to counter new threats. In some cases, where guns did stay for a while sites were provided with a waist high concrete block wall with crew and predictor shelters and ammunition lockers. At least three of this type of emplacement has been identified at Lowestoft. Some light machine guns at Bawdsey CH Station were also provided with simple sunken brick built emplacements with a crew shelter. The need for a LAA gun to have a good all round view and open field of fire required some guns allocated for defence of coastal towns to be mounted on rooftops - for example at Lowestoft two Bofors guns were sited on the roof of Pryce’s Warehouse, one on the Co-op Factory roof and one on the roof at Waller’s Restaurant at Oulton Broad. LAA gun (20mm) mounts were sometimes added to the roof of pillboxes and the Type 23 pillbox was specifically designed with both an infantry chamber and a AA light machine gun chamber.
Top left: Sunken brick built emplacement for a light machine gun for
use in AA role - Bawdsey CH Station. Right - mount for a 20 mm AA
gun, probably an Oerlikon 20mm, Bawdsey CH Station. Bottom left -
an Oerlikon 20mm on a AA mount (photo taken in USA).
Ack-Ack, General Sir Frederick Pile, G.C.B., D.S.O., M.C, Panther Books, 1956
AADC Harwich papers, TNA
6th AA Division papers, TNA
57 AA Brigade papers, TNA
Manual of Anti-Aircraft Defence, Vol II, Employment, Pamphlet No. 1 Principles, Characteristics and Lay-outs, The War Office, Jun 1940
Fortress Lowestoft, R Jarvis, The Heritage Workshop Centre, 2002
AA Command, C Dobinson, Methuen, 2001