Click here to Hear this gun fire

Sweden
Bofors 40mm Model 1936
--
United States of America
40mm Caliber Mark 1 and Mark 2
--
British
40mm Caliber QF Mark IV, NI, NI/I, IX and X
--
German
40mm Flak 28
--
Japanese
40mm Type 5


One of the best Heavy MG AA weapons of WWII, the Bofors 40mm Model 1936 is still in service in some nations.  This weapon was used on almost every US and UK warship of WWII and was a very potent AA gun.  The Germans also used the Bofors design to develop the 40mm Flak 28 and the Japanese copied a British Army type Bofors captured at Singapore to produce the 40mm Type 5.

In 1941, BuOrd contracted for USA manufacturing.  First shipboard installation in the USA was in the summer of 1942.  Total USA production was about 39,200 weapons.  The Gridley class destroyers were the only first-line destroyers in the USN not to receive this weapon.  Early versions used friction-coupled drives, which rapidly wore out due to salt contamination.  Later versions built in the USA used hydraulic-coupled drives which eliminated the problem.

Naval single mounts were air cooled, naval twin and quadruple mounts were water cooled.  A modification kit is now available to increase the rate of fire to 180 rounds per minute and the magazine capacity to 20 rounds in a banana feeder fed by standard 4 round clips.

The Mark 51 director system gave the USA weapons unmatched accuracy.  For example, half of all Japanese aircraft shot down between 1 October 1944 and 1 February 1945 were credited to the Bofors/Mark 51 combination.  See the article on the Mark 51 director at our Technical Board.

The Mark 1 is a left-hand weapon and the Mark 2 is a right-hand weapon.  Unless otherwise noted, the data that follows is for the USA Mark 1 and Mark 2 versions, but weapons built by other nations had similar performance.

   
Gun Characteristics
 
Designation 40mm/56 (1.57") Mark 1 and Mark 2
Ship Class Used On Almost all
Date Of Design 1941
Date In Service 1942
Gun Weight about 1,150 lbs. (522 kg)
Gun Length oa 98.4 in (2.499 m) (overall)
Bore Length 88.6 in (2.250 m)
Number Of Grooves 16
Length Of Rifling USA:  75.85 in (1.927 m)
German:  76.06 in (1.932 m)
Chamber Volume 28.3 in3 (0.464 dm3)
Rate Of Fire 120 rounds per minute per barrel nominal 
140-160 rounds per minute when horizontal (gravity assist)
    
Ammunition
 
Type Fixed
Weight of Complete Round USA - 4.75 lbs. (2.15 kg)
UK - 4.88 lbs. (2.21 kg)
Others - N/A
Projectile Types and Weights USA
   HE - 1.985 lbs. (0.900 kg)
   AP - 1.960 lbs. (0.899 kg)

UK
   HE - 1.97 lbs. (0.894 kg)
   SAP - N/A

German
   HE - 2.105 lbs. (0.955 kg)

Japan
   HE - 2.2 lbs. (1.0 kg)

Bursting Charge USA - 3.39 oz. (96 g)
Overall Length USA - 17.62 in (44.75 cm)
UK - 17.75 in (45.1 cm)
Others - N/A
Propellant Charge USA - 0.694 lbs. (0.314 kg)
UK - 0.719 lbs. (0.326 kg)
Germany - 0.668 lbs. (0.303 kg)
Japan - 0.661 lbs. (0.3 kg)
Muzzle Velocity USA Marks 1 and 2:  2,890 fps (881 mps)
UK Mark NI:  2,720 fps (829 mps)
Germany Flak 28:  2,801 fps (854 mps)
Japanese Type 5:  2,953 fps (900 mps)
Working Pressure USA - 19.5 tons/in2 (3,070 kg/cm2)
UK - 19.68 tons/in2 (3,100 kg/cm2)
Others - N/A
Approximate Barrel Life USA - 9,500 Rounds
UK - 10,000 Rounds
   
Range  
Elevation With 1.985 lbs. (0.900 kg)
HE Mark 2 Shell
With 1.960 lbs. (0.899 kg)
AP M81A1 Shell
Range @ 10 degrees 6,844 yards (6,258 m) 6,466 yards (5,913 m)
Range @ 15 degrees 8,227 yards (7,523 m) 7,580 yards (6,931 m)
Range @ 20 degrees 9,295 yards (8,499 m) 8,389 yards (7,671 m)
Range @ 25 degrees 10,103 yards (9,238 m) 8,959 yards (8,192 m)
Range @ 30 degrees 10,691 yards (9,776 m) 9,358 yards (9,358 m)
Range @ 35 degrees 11,057 yards (10,111 m) 9,568 yards (8,749 m)
Range @ 40 degrees 11,208 yards (10,249 m) 9,618 yards (8,795 m)
Range @ 45 degrees 11,133 yards (10,180 m) 9,492 yards (9.679 m)
AA Ceiling 22,299 feet (6,797 m)  N/A
Notes:  Most USA produced ammunition was set to detonate at 4,000-5,000 yards (3,700-4,570 m) so as to minimize damage due to "friendly fire."  British rounds self-destructed at 3,000-3,500 yards (2,700-3,200 m) but this could be increased to 7,000 yards (6,400 m) in some ammunition types.
    
Data from:

www.NavWeaps.com


"Joining the War at Sea" by Franklyn E. Dailey Jr., Capt. USNR (Ret.)
"German Cruisers of WWII" by M. J. Whitley
"US Battleships:  An Illustrated Design History" and "1991-92 Naval Institute Guide to World Naval Weapon Systems" both by Norman Friedman
"Naval Weapons of WWII" by John Campbell
"Radar at Sea" by Derek Howse
"Warship Volume III" article by Lawrence Sowinski
Special help from Mark Fitzpatrick and Cliff McMullen


"Click Here" for additional Information on

Later model 20MM and 40MM guns.