The first equipments were imported from Sweden in 1937. Before the outbreak of War, manufacture had started in Britain and during the first months of the War was augmented by imports from Sweden, Poland etc. Subsequently equipments were also produced in Canada and America.
The gun went through considerable modifications during the War, including remote power for operation with the Kerrison Predictor (No. 3) and various modifications to the travelling platform, autoloaders and sights.
For Land Service, the gun was mounted on four-wheeled towed platforms, and later in the War on S.P Morris chassis, in Crusader tanks etc. In Naval service, guns were mounted in single, twin or six barrel mountings.
When deployed in the LAA role, guns were sited singly, but sufficiently close together to permit a great volume of fire to be brought onto low attacking low flying aircraft and dive bombers. Fire was controlled by Kerrison Predictor, Stiffkey Stick or AA Cartwheel sights. Although the Kerrison Predictor was considered to be “outstandingly ahead of any other method of aiming a light anti-aircraft gun that existed – even in the German Army”, it was of limited use against “Tip and run” raids where the Bofors gun could not be traversed quickly enough against such fleeting targets and reliance was placed on open sights or Stiffkey Sticks. Normal crew for land service was a Detachment Commander and six men for direct laying and a Detachment Commander and eight men for predictor control. With direct laying the gun could be operated by just three men.
The gun could fire High Explosive (fitted with Percussion Direct Action fuze, tracer and self-destroying element which destroys the shell if no direct hit was obtained) used for AA engagements or Armour Piercing rounds used against Armoured Fighting Vehicle’s etc. In addition to its normal LAA role, it proved useful in providing “pointer fire” to guide attacking infantry at night, against light AFV’s and breaching barbed wire defences.
The effective range was limited by the type of fire control and the range at which self destruction of the shell occurs (between 3,400 yards and 5,500 yards depending on the type of tracer used). In a LAA role, the effective range was 1,500 yards but in special circumstances harassing fire could be employed against targets up to the range of self-destruction of the shell. The maximum range at which AFV’s were normally engaged was 400 yards. The maximum rate of fire was 120 rpm (at “Auto”). Normal rate was 60 to 90 rpm (at “Single Shot”). Single shot was normally used with Predictor Control and Auto against fleeting targets which suddenly came into view and gave no opportunity of laying the gun.
Above: Left and middle - Bofors 40mm gun on four wheeled platform, manufactured by Metropolitan-Vickers. Right - Bofors 40mm gun and
Notes on Anti-Aircraft Artillery, Military College of Science Publication, 1944
Ack-Ack, General Sir Frederick Pile, G.C.B., D.S.O., M.C, Panther Books, 1956