The Bofors 40mm gun was first developed in the early 1930s, in response to a 1928 request by the Swedish Navy for a ship-mounted anti-aircraft weapon. The firm developed automatic guns in caliber ranging from 20mm to 57mm, but the 40mm because a tremendous commercial success. They were used by many nations on both sides of World War II in both naval and ground applications, and the gun is still in use to this day.

In the US, production was done by the Chrysler corporation during the war. The Bofors design was a very complex one, and originally used a lot of hand fitting in assembly. Chrysler was unable to simplify the design, but was able to dramatically reduce manufacturing time by changing to more production-friendly methods (like the use of cast and powder-metal parts instead of all milled components) and the use of fully interchangeable parts.

The ground variant was typically a single gun mount and air-cooled, while Naval guns used a water cooled jacket around the base of the barrel and were generally mounted in pairs and quartets. Modern versions use powered magazines capable of firing up to 330 rounds per minute.

Manuals (English)

40mm Bofors AA gun manual (US Navy, 1943)
40mm Bofors AA gun manual (US Navy, 1943)

Resources has an interesting article on the Chrysler manufacturing of the 40mm Bofors.


  1. Great manual…excellent drawings !!!
    Seems like it’s not just a manual but a thorough book about this gun !

    • I have a brass plaque that says 40 mm Machine Gun Mech. Mark 2, Mod. 1, Inspector NCG, serial No. 36925 Chrysler Corporation Detroit, Mich. weight 778 LBS,1943

  2. Hello,
    Maybe you can make a video of a long forgottened Webley revolver,many pistols has been shown but nothing on Colt45,Webley Revolver models,Nagant revolver and other Revolver models…

    Only pistols had been explained here…

  3. Twin Bofors were even mounted on to an M41 Light tank. This produced the M42 “Duster”, antiaircraft platform.

  4. An interesting manual…

    The breech mechanism on the L60 seems to be significantly different to one I recall on the L70 which I played with in the late 60’s..

    I recall the L70 had a long loading tray which pivoted down from the rear of the breech mechanism, which does not seem to be present on the L60.. am I right or just dreaming?

    Also, as I recall, you had a long tool known as “the samouri sword” which you fed through a hole in the rear of the breech to extract the round sitting in the breech mech when you stopped firing or when you had a misfire…

    • Cancel my last…

      Just spotted the loading tray!

      The only difference I can see (apart from the L70 being a single barrel) is there was a lever on the magazine cams that you used to force the round down into the hopper.

      We used L40/70s in the 1960s in the UK for reserve AA. The Navy still had 40/60 on some of their ships and there was loads of 40/60 ammo about. We had spare barrels and breech blocks for the 40/70s that llowed the use of 40/60 ammo, which was a good thing as the 40/70 HE fuzes were banned for use as they were not raindrop safe. We only had plugged HE for range practice which exploded on traced burnout. We had proper fuzed L60 HE shell, buto only ever used it at ground targets!

  5. I served with the RAF 103 MU (maintainence Unit) servicing L40/70 Bofors for the RAF REGIMENT LAA (Light Anti-Aircraft) WING at RAF AKROTIRI CYPRUS in the early 60’s As I remember it they were fitted to an electo-hydraulic platform driven by a BAUSCHER (?) Two stroke unsilenced diesel engine /generator. The platform was similar in design to the BOULTON-PAUL aircraft gun turret I’m told and was later also used as a mounting platform for the BLOODHOUND Ramjet (TWIN THOR RAMJETS) powered heavy AA missile’
    I also served on the BLOODHOUND unit at RAF WOOLFOX LODGE just outside STRETTON on the AI Motorway In the BOFORS ROLE the platform could be radar controlled in multiples. The fact that radar was not used always led us to believe that it’s real purpose in CYPRUS was as a super heavy ground defence cannon. For those out there that can remember the Regiment used BOFOR ISLAND of CAPE GATTA at AKROTIRI for Ground Defence traing and an ancient METEOR DROGUE tug for the AA role. Such was the marksmanship of the Regiment that more than one tug pilot had ”brown jobbbies” once in a while. I also remember rthat at the time the Royal Artiller in MALTA were equipped with the L40/60 The difference was. I believe in the length of the barrel and less powerful ammo and the 40/60 was all manually operated

  6. The Army’s 40/60s were manual, but I think were pretty well all replaced by 40/70 in the late 50s, although there may have been some scattered around. As I said before, the Navy used 40/60 up to the 70s so Malta may have been the exception, although all 40/70s were issued with 40/60 barrels and breeches.
    The 40/70 was fitted to the same mounting as the Thunderbird missile. I think the mount for the Bloodhound was similar, but much larger. The Army used 27.5 kVA Meadows generators to power these..

    • I have registered rings and blocks for a Mk1 mount, or two Mk3 (Army) mounts (40mm/L60)… But I need a non-demilled L60 barrel so I can put it on a sand stand and fire off a round. Not sure if the water-cooled barrels run without it when not firing for sustained periods. Bought two breech rings and blocks semi-blind out of an estate inventory that no one would quite recognize. Fortunately I have a silly amount of military reference material and winkled them out fairly quick. I have the right and left receivers for Machinegun, 40mm, Mk1 (mods 0 through 3) and Mk2 (mods 0 through 3). The only thing I’m NOT yet sure of is which specific mark it is. The only thing I’m worried about is if they were amnesty registered as DD’s after the MG cutoff date, and their formal designation is Machinegun, 40mm, though today they’d be more properly called auto cannon.

      I figured this for a short cannon restore project, but those type 1 mounts are as complex as a car. More complex than a car of the period. Building out as two Mk3 Army mounts would be easier, but when I realized what i might have I snagged the second block as soon as the guy offered it.

    • 40mm bore diameter and a barrel length equal to 60 times the bore diameter (which would be 2.4 meters in this case). That is a standard way to describe barrel length on cannons.

      • Note that thought the sea version was listed an L60 it really was only about 54 calibers in length or so with the water cooled barrel in the Mk1 and Mk2 turrets. Those old breeches can take 40mm/L70 if you put the right barrel on.

  7. Greetings from Columbiana Ohio,
    My Employer is developing the Harvey Firestone Homestead. We are working
    on creating a museum honoring the Firestone Legacy. I am working on the
    Firestone War effort. Firestone Tire and Rubber Company redesigned an built
    the Carriages and mounts for the Bofors guns. As I’m sure you know, the
    Bofors were used by both Army and Navy. We are looking for assistance on how
    to verify the manufacturer of a quad mount Bofors used on a U.S. Navy
    Vessel. Any help would be greatly appreciated.
    Ken Rambo

    • I have a 40mm WWII Bofors on a Firestone mount and trailer that I WOULD CONSIDER LOANING THE MUSEUM for some years…..until you can find one to buy to get a donation of one. Call me at 505-269-2056 to discuss
      Mine is mostly restored with the correct and original data plates. I occasionally tow it behind my M3a1 Scout Car in parades. Need a few things addressed to be fully functional on the mount and trailer.

  8. All the actual breech mechanisms were made by York Safe and Lock Co, somewhere in PA. We built them at first under the table, then arranged a manufacturing license. They were made from ’42 to ’44 at which time naval ships were switching to the 3″/50 caliber gun with proximity fuzes, which were far more effective.

  9. Feels strange looking at this old cannon. Where i live, just down the road, we have an AA mounted in front of the RSA(Returned Servicemen’s Association) though it might be a different model. It still moves like the day it was made after nearly 80 years of neglect as a monument in a garden. I used to spin the handles and spin around the gun though they locked the vertical traverse to prevent people freaking out about a 40mm cannon pointing at their car. To my knowledge the action still works but they concreted the barrel.

    • On closer look of the Manual it was a later model. Also I’ve been corrected that after the war it was stored for about a decade or so before it was donated to the RSA with the concreted barrel.

  10. Hi Does anyone have design drawings/blueprints of the bofor 40mm LAA gun like the one that was used in malta during ww2? really would like to get my hands on them.

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