40 mm Bofors Light Anti-Aircraft Gun

The Swedish company Aktiebolaget Bofors developed the gun in the late 1920’s and began international sales in 1931. By the start of World War 2, it was in use in 18 countries. In Britain, the War Office decided in April 1937 to purchase 100 guns & ammunition from Sweden and negotiated a license to build them in Britain. In the interim, more guns were purchased from Poland who where building them under license for export. Thereafter, Britain developed her own variations and the guns were manufactured here and in Canada.

The Kerrison Predictor (No. 3) was produced for the gun, the auto-loader simplified and several differnet sights were developed. Near the end of the war, remote power control was perfected. The gun was designed to be lowered to the ground for firing but it could be fired from its wheels, or even on the move if necessary.

Gun

Mark 1Original Swedish make. Used Type A auto-loader
Mark 1*Similar to Mk1 but could use any auto-loader
C Mark 1Mk1 but Canadian made
C Mark 1*Mk1* but Canadian made
Mark 1/2Conversion of Mk1* by removing flame guard from muzzle & fitting
double baffle muzzle brake. For airborne mountings Mks7 to 10
Mark 2Naval design but number withdrawn to avoid confusion with
American M2 model
Mark 3Wartime production model for simplified auto-loader
Mark 4Naval, water cooled for twin mounting
Mark 5Naval, water cooled for single mounting
Mark 6As Mk1 but with changes for mounting in tanks. Used with Mounting Mk6
in Crusader AA Tanks. Cartridge deflector ejected upwards
Marks 7 to 11Naval patterns
Mark 12As Mk1 but withcut out switches on the elevating arc. For remote power
control mountings
Mark 12/1C Mk1 modified as for Mk12

Auto-loaders

Type ASwedish pattern with central guide & 10 mechanical feed pawls. Took
two 4 round chargers, empty chargers ejected to left of breech casing
Type A*Type A with adjustable peep sight in rear guard. Used only on Mk6 gun on tanks
Type BSimplified design, no central guide. Took three 4 round chargers ejecting
to the right
Type CNon-standard variation of Type B made by the Chambon Company
Type MType B modified to be more reliable
Type M*Type C modified to be more reliable

Mountings

Mark 1Original Bofors design. Direct laying, prepared for data receiving dials
but not fitted
Mark 1APolish design. As Mk1 but not prepared for dials
Mark 1BBritish design. Similar to Mk1 but with elevatin & traversing gears designed
for hand or power operation. Only 2 made
Mark 2Mk1 modified for remote power control. None made
Mark 3British design. for remote power control
C Mark 3Canadian manufactured Mk3
Mark 3AAs for Mk3 but small changes in hand controls
Mark 3BAs for Mk3A but with modified platform
Mark 4Similar to Mk3B but with “cease firing” switches to prevent inadvertent
firing at dangerous elevations
Mark 4AAs Mk4 but with elevating & traversing gears made by Linotype Company
Mark 5As Mk4 but modified for mounting on Morris SP Carrier
C Mark 5Canadian manufactured Mk5
Mark 5/1Mk5 with remote power control removed
Mark 6Similar to Mk4 but modified for use in Crusader AA Tanks
Mark 7Mk3 converted to fit airborne 2 wheel carriage
Mark 8Mk4 converted to fit airborne 2 wheel carriage
Mark 9C Mk3 converted to fit airborne 2 wheel carriage
Mark 10Mk4 Canadian manufactured, converted to fit airborne 2 wheel carriage

Platforms (Carriages)

Platform Mark 1Original Bofors design. Rivetted girder construction,
Ackerman steering, independent suspension, 6 x 20 inch
tyres, hydraulic brakes on rear wheels
Platform Mark 1APolish design. Similar to Mk1 but with 5 wheel studs not 6
Platform Mark 2British design. Tubular side girders, trolley steering,
9 x 13 inch tyres, no springing
Platform C Mark 2Canadian manufactured version of Mk2
Platform Mark 3Similar to Mk2 but with mechanical over-run brakes
on front wheels
Platform Mark 4Mk2 converted for stowage in aircraft or gliders. Could
be broken down into 10 units
Platform 2 Wheeled C Mark 1Canadian design. Light, sprung platform for air
transportation or jeep towing. 2 hinged girders formed
a tow bar & a 3rd telescoped into the centre
Carriage, transporting
Mark 1/India
2 wheeled carriage, for air transportation & Jeep towing
For use in Far East. For Indian Army use
Carriage, transporting
Mark 2/India
As Mk1 but lighter, without brakes & axle 6 inches shorter
Carriage, transporting Mark 2/1As Mk2 but with brakes. For British Army use in Far East
Holdfast Mark 1For concrete emplacement. 4 steel beams with with
8 hold down bolts
Platform Firing Mark1Temporary wood structure for emergencies
Platform Firing No. 16Steel platform for use with Mk3 mounting in Maunsell Forts

Self Propelled Mountings

Carrier Morris, 40mm AA Mk 1A 3 ton Morris Commercial truck chassis with Mk5 mounting secured
to the cargo bed
Crusader III, AA Tank, Mk 1Crusader III with turret removed replaced by an armoured barbette carrying the gun. Control was by hydraulic power with one operator using a joystick for elevation & traverse

Crew

No. 1Detachment Commander Sergeant
No. 2Layer Line
No. 3Layer Elevation
No. 4Loader & Firer
No. 5Ammunition
No. 6Ammunition
No. 7Detachment 2 i/c Bombardier

Data

Mark 1 Gun on Mounting Mark 1

Weight of Gun & Breech Mechanism966 lbs
Total Length117.7 inches
Length of Bore88.58 inches (56.25 calibres)
Rifling16 grooves, increasing right hand twist, 1/54 to 1/30
Breech MechanismVertical sliding block, automatic, percussion fired
Elevation-5° to +90°
Traverse360°
RecoilHydro-spring, constant 7.87 inches
Weight in action4,368 lbs
Rate of Fire120 rounds per minute

Performance

Firing standard 2lb HE Shell

Muzzle Velocity2,700 feet/second
Maximum Horizontal Range10,800 yards
Maximum Ceiling23,600 feet
Effective Ceiling5,000 feet

Ammunition

Shell, HE, Mark 4TStreamlined 2 lb shell using Fuze Percussion No. 251 or 255
Shot, AP, Mark 6TPlain steel shot with internal tracer
Propelling ChargeCordite in a brass case with various percussion primers.