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 as the 40 mm Bofors Light Anti-Aircraft Gun. 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 1 | Original Swedish make. Used Type A auto-loader |
| Mark 1* | Similar to Mk1 but could use any auto-loader |
| C Mark 1 | Mk1 but Canadian made |
| C Mark 1* | Mk1* but Canadian made |
| Mark 1/2 | Conversion of Mk1* by removing flame guard from muzzle & fitting double baffle muzzle brake. For airborne mountings Mks7 to 10 |
| Mark 2 | Naval design but number withdrawn to avoid confusion with American M2 model |
| Mark 3 | Wartime production model for simplified auto-loader |
| Mark 4 | Naval, water cooled for twin mounting |
| Mark 5 | Naval, water cooled for single mounting |
| Mark 6 | As Mk1 but with changes for mounting in tanks. Used with Mounting Mk6 in Crusader AA Tanks. Cartridge deflector ejected upwards |
| Marks 7 to 11 | Naval patterns |
| Mark 12 | As Mk1 but withcut out switches on the elevating arc. For remote power control mountings |
| Mark 12/1 | C Mk1 modified as for Mk12 |
Auto-loaders
| Type A | Swedish 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 B | Simplified design, no central guide. Took three 4 round chargers ejecting to the right |
| Type C | Non-standard variation of Type B made by the Chambon Company |
| Type M | Type B modified to be more reliable |
| Type M* | Type C modified to be more reliable |
Mountings
| Mark 1 | Original Bofors design. Direct laying, prepared for data receiving dials but not fitted |
| Mark 1A | Polish design. As Mk1 but not prepared for dials |
| Mark 1B | British design. Similar to Mk1 but with elevatin & traversing gears designed for hand or power operation. Only 2 made |
| Mark 2 | Mk1 modified for remote power control. None made |
| Mark 3 | British design. for remote power control |
| C Mark 3 | Canadian manufactured Mk3 |
| Mark 3A | As for Mk3 but small changes in hand controls |
| Mark 3B | As for Mk3A but with modified platform |
| Mark 4 | Similar to Mk3B but with “cease firing” switches to prevent inadvertent firing at dangerous elevations |
| Mark 4A | As Mk4 but with elevating & traversing gears made by Linotype Company |
| Mark 5 | As Mk4 but modified for mounting on Morris SP Carrier |
| C Mark 5 | Canadian manufactured Mk5 |
| Mark 5/1 | Mk5 with remote power control removed |
| Mark 6 | Similar to Mk4 but modified for use in Crusader AA Tanks |
| Mark 7 | Mk3 converted to fit airborne 2 wheel carriage |
| Mark 8 | Mk4 converted to fit airborne 2 wheel carriage |
| Mark 9 | C Mk3 converted to fit airborne 2 wheel carriage |
| Mark 10 | Mk4 Canadian manufactured, converted to fit airborne 2 wheel carriage |
Platforms (Carriages)
| Platform Mark 1 | Original Bofors design. Rivetted girder construction, Ackerman steering, independent suspension, 6 x 20 inch tyres, hydraulic brakes on rear wheels |
| Platform Mark 1A | Polish design. Similar to Mk1 but with 5 wheel studs not 6 |
| Platform Mark 2 | British design. Tubular side girders, trolley steering, 9 x 13 inch tyres, no springing |
| Platform C Mark 2 | Canadian manufactured version of Mk2 |
| Platform Mark 3 | Similar to Mk2 but with mechanical over-run brakes on front wheels |
| Platform Mark 4 | Mk2 converted for stowage in aircraft or gliders. Could be broken down into 10 units |
| Platform 2 Wheeled C Mark 1 | Canadian 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 2/1 | As Mk2 but with brakes. For British Army use in Far East |
| Holdfast Mark 1 | For concrete emplacement. 4 steel beams with with 8 hold down bolts |
| Platform Firing Mark1 | Temporary wood structure for emergencies |
| Platform Firing No. 16 | Steel platform for use with Mk3 mounting in Maunsell Forts |
Self Propelled Mountings
| Carrier Morris, 40mm AA Mk 1 | A 3 ton Morris Commercial truck chassis with Mk5 mounting secured to the cargo bed |
| Crusader III, AA Tank, Mk 1 | Crusader 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. 1 | Detachment Commander Sergeant |
| No. 2 | Layer Line |
| No. 3 | Layer Elevation |
| No. 4 | Loader & Firer |
| No. 5 | Ammunition |
| No. 6 | Ammunition |
| No. 7 | Detachment 2 i/c Bombardier |
Data
Mark 1 Gun on Mounting Mark 1
| Weight of Gun & Breech Mechanism | 966 lbs |
| Total Length | 117.7 inches |
| Length of Bore | 88.58 inches (56.25 calibres) |
| Rifling | 16 grooves, increasing right hand twist, 1/54 to 1/30 |
| Breech Mechanism | Vertical sliding block, automatic, percussion fired |
| Elevation | -5° to +90° |
| Traverse | 360° |
| Recoil | Hydro-spring, constant 7.87 inches |
| Weight in action | 4,368 lbs |
| Rate of Fire | 120 rounds per minute |
Performance
Firing standard 2lb HE Shell
| Muzzle Velocity | 2,700 feet/second |
| Maximum Horizontal Range | 10,800 yards |
| Maximum Ceiling | 23,600 feet |
| Effective Ceiling | 5,000 feet |
Ammunition
| Shell, HE, Mark 4T | Streamlined 2 lb shell using Fuze Percussion No. 251 or 255 |
| Shot, AP, Mark 6T | Plain steel shot with internal tracer |
| Propelling Charge | Cordite in a brass case with various percussion primers. |