The first of the famous Bofors automatic guns, this version was the first one ordered by the Swedish military and was designed for submarine use. The gun and mounting was designed to be lowered into a water-proof tubular compartment under the decking. This was accomplished by elevating the gun to 90 degrees and then folding the fire-control handles and spent-cartridge chute up against the gun.

This weapon was very similar in design to the later Bofors 40 mm/60 gun and used the same ammunition as that did that gun but with a reduced propellant load.

Non-folding single and twin mounts were produced and exported to Poland, but the Royal Swedish Navy used only the single folding mount.

The last Swedish submarine with this gun was decommissioned in 1966.

Gun Characteristics

Designation 40 mm ubätsautomatkanon M/32
Ship Class Used On Sjölejonet and Neptun classes
Exported to Poland
Date Of Design 1930
Date In Service 1932
Gun Weight 243 lbs. (110 kg)
Gun Length about 67.7 in (1.72 m)
Bore Length N/A
Rifling Length N/A
Grooves 16
Lands N/A
Twist Increasing RH twist
Chamber Volume N/A
Rate Of Fire 120 to 140 rounds per minute cyclic
80 to 90 rounds per minute practical


Type Fixed
Projectile Types and Weights AB 40 mm L/60 HE-T: 2.05 lbs. (0.93 kg) 1
Weight of Complete Round about 4.41 lbs. (2.0 kg)
Bursting Charge HE-T: about 0.150 lbs. (0.068 kg) TNT
Projectile Length 7.25 in (18.4 cm)
Complete Round Length 17.60 in (44.7 cm)
Cartridge Case Type, Size and Empty Weight Brass, 40 x 311R, 1.93 lbs. (0.88 kg)
Propellant Charge 0.485 lbs. (0.220 kg)
Muzzle Velocity 2,297 fps (700 mps)
Working Pressure N/A
Approximate Barrel Life N/A
Ammunition stowage per gun N/A
  • ^As noted above, this was the same ammunition as produced for the Bofors 40 mm/60 but with a reduced propellant charge. Rounds were self-destructing.


Range with 4.41 lbs. (2.0 kg) HE-T
Elevation Distance
Max Horizontal Range
about 4,800 yards (4,370 m)
Max Possible Horizontal Range
(no self-destruct)
about 10,900 yards (9,980 m)
Max Vertical Range
about 14,650 feet (4,460 m)

Mount/Turret Data

Designation Single Folding Mounts: Sjölejonet (2) and Neptun (1)
Weight Single Mount: about (900 kg)
Twin Mount: 6,173 lbs. (2,800 kg)
Elevation -10 to +90 degrees
Elevation Rate N/A
Train 360 degrees
Train Rate N/A
Gun recoil N/A


Data from:

  • "The Bofors Gun" by Terry J. Gander

Page History

30 December 2015
New datapage