Bofors 37mm AT Gun (Video)

The Swedish Bofors company developed a sophisticated and very high-quality light anti-tank gun in the early 1930s, and found significant commercial success with it. A variety of countries either purchased the guns outright from Bofors or paid for licenses to produce them domestically. These countries included Denmark, Finland, Poland, the Netherlands, and Sweden itself. The largest number were in Poland (1200 or more), and there is speculation that some may have been sold to Spain during the Spanish Civil War (both these guns and a 40mm AA gun which definitely went to Spain were designated wz.36). A significant number were also captured and reused by German and Russian forces during WWII. On the Allied side, some of the guns were sold to the Sudan and used by British forces in North Africa (generally mounted on trucks).

The gun itself was an excellent design, capable of 12 rounds/minute of accurate fire and potent enough to deal with most of the smaller tanks in existence at the beginning of WWII. New tank developments made it obsolete, but it was at least effective against Russian light tanks (BT, T-26, T-28) in the Winter War if not the heavier T-34s. The gun has a sophisticated suspension system to help absorb recoil energy, and fired a 37x257mm shell with a 740g projectile at about 825 m/s (26oz @ 2700 fps). The action was semi-automatic, meaning that once fired, the action would recoil on the carriage, and automatically eject the empty case. It would then return to battery with the breech open, ready for a new shell to be loaded (in the video, the ejection mechanism has been disabled to help preserve the brass cases).

 

40 Comments

  1. That was a very popular class of weapon at the start of the war – the US would use the M3, M5 & M6 37mm guns through out the war even though it’s 37×223 mm R round was obsolete by the time even the “Honeys” armed with it began fighting with the British.

    Like the arty posts. Please keep them up.

    • The US 37mm AT/tank gun was the best of the 37mm guns. While it fired a somewhat weaker round that the Bofors, its very long barrel more than made up for the difference. Then again, the British 2-pounder was even better with only a marginally larger caliber (40mm).

      • One reason the u.S. 37mm was superior was its greater MV; about 2900 FPS with AP shell and as much as 3,100 FPS with AP shot. This was due to two differences it had with the German 3.7cm PAK it was partly based on. First, it’s cartridge case was a true bottlenecked one, rather like an enlarged .30-30 Winchester or .32 Winchester Special case, rather than the slightly-tapered straight-wall case used by the German, British, and many other AT guns in its caliber range;

        http://www.inert-ord.net/usa03a/usa5/37mm/6946s.jpg

        The German rounds are on the right, the U.S. rounds on the left in the picture.

        (The Bofors 37mm was an exception to this.)

        The other reason was that U.S. propellant powder, notably the DuPont powder used in most U.S. artillery ammunition, was faster-burning and generated higher pressures than the propellant powders used by European powers. They preferred “double-base” powders in the belief that they were somehow safer in storage; the destruction of HMS Hood in the Denmark Strait showed this to be a rather inaccurate, and dangerous, assumption.

        The U.S. forces, by comparison, used single-based powders which were less potentially deflagrative in storage but which had a shorter (theoretical) safe storage life, on the principle that U.S. makers like DuPont and Remington had raised their power potential to a higher level through research for purely commercial (sporting) uses. In short, U.S. powders had a shorter shelf life, but gave more bang for the cartridge-load.

        When the Stuart “Honey” showed up in the Western Desert, both the British and the Axis forces were surprised. Not only at its greater mechanical reliability compared to the British “cruiser” tanks, but also because its 37mm AP shot would penetrate the front plate of a Panzer III Ausf. E at about 600 yards, vs. no further than 300 for the 2-pounder on the A-13, Crusader 1, or Matilda 2.

        Since the 37mm on the Panzer III would penetrate the frontal aspect of A-13 or Crusader out to 400, and the 5cm on the later versions would do it at 600, the Germans were less than pleased to see the Honey enter the fray.

        It’s probably fortunate that the Wehrmacht didn’t pay much attention to the Bofors 37mm. Imagine Panzer IIIs armed with 3.7cm guns firing the Bofors gun’s round.

        Ouch.

        cheers

        eon

        • You are right about the cartridge and powder differences, but the main advantage of the US 37mm was still its much longer barrel. The M3 towed AT gun and the M6 tank gun 37mm L/53.5 barrel, in other words 1,980mm. The M5 tank gun had a slightly shorter 37mm L/50 barrel (1,850mm). The PaK 35/36 had a 37mm L/45 barrel, that is, only 1,660mm.

          The Bofors 37mm AT gun really was better than the German Pak 35/36, but the difference was not drastic in practice. Both became instantly obsolescent once the T-34 entered the scene. The Germans also had tungsten APCR projectiles for their gun, which never existed for the Bofors gun

          By the way, HMS Hood was sunk when her aft 4″ magazine was penetrated by a projectile and exploded. Alternatively fire may have reached the same magazine indirectly. In any case, the big gun warships carried so much artillery shells, that the chances of survival after either possibility were practically nil, no matter what the powder was.

          • Actually, the Royal Navy’s board of inquiry concluded that it was the 15″ powder magazine for X and Y turrets that ignited and that the cordite-based propellant was the culprit;

            It must be noted however, that British double-based propellants, which contained a substantial amount of nitroglycerine in their makeup, were significantly more susceptible to ignition than their single-base American counterparts. In 1945 the U.S. Navy Bureau of Ordnance conducted systematic tests to determine the susceptibility of various propellant formulations to accidental ignition.

            Using a nozzle mechanism capable of generating a reproducible flash, they found that while British Cordite type propellants would ignite while still some 530mm from the vent, standard American single base propellants would not ignite until the distance was reduced to 120mm, and the relatively new U.S. “SPCG” flashless powder, incorporating nitroguanadine, would have to be within 25mm of the nozzle before ignition took place. These are very substantial differences.

            Assuming the flame of the explosion to expand in a spherical front, the same explosion which would ignite one cubic unit of standard American powder, would be capable of igniting almost seventy-five times as much cordite. In the confined space of a magazine, the relative amounts of gas evolved, and the ensuing internal pressures could easily spell the difference between disturbance and disaster.

            Had Hood carried single base propellant instead of cordite, there is in fact a good possibility that the fatal explosion might never have occurred.

            http://www.navweaps.com/index_inro/INRO_Hood_p3.htm

            cheers

            eon

          • If you had read the whole article, you would have noticed that the author also concluded that the explosion most likely started in the aft 4″ magazine : http://www.navweaps.com/index_inro/INRO_Hood_p4.htm

            Even more importantly, there was an expedition to the hull in 2001, and the evidence from that does not support any other theory than explosion in the aft magazine(s): http://www.hmshood.com/hoodtoday/2001expedition/hood/encrypt.htm

            It is impossible to determine if it was the 4″ or 15″ aft magazines that exploded first, but the 4″ seems to have been the more likely origin. The 4″ shells were more vulnerable to symphathetic detonation and they were closer to the area where most eye witnesses placed the first signs of explosion.

            But yes, it is possible that the higher volatility of the British cordite propellant might have contributed to the catastrophic magazine explosion, although that is impossible to prove without knowing the exact conditions of the primary explosion produced by the penetrating shell.

    • The Finnish army had no less than six different armor piercing projectiles for the Bofors gun, four APHE shells and two AP (solid shots) projectiles. The solid shots were manufactured in Finland, the rest were either Swedish or Polish in origin. Projectile weight was either 740g or 700g and muzzle velocity varied from 810 m/s to 830 m/s. The Soviet test values for the 700g Polish projectiles appear rather low, but quite possible.

  2. wow very nice piece in same caliber as my pak i would like to talk this cannon guy about reloading my pak 36 cases (having a dificult time removing primers etc)

  3. Wow very nice Iam a fan of artillery on gun auction they have bofors 40 mm debates for sale but located in different countries I wish there where some in the USA I think so as scrap where to find them I have a bunch of Oerlikon barrels never used and two never used Bofors barrels I am a collectors of vintage stuff great website thanks

  4. As usual at FW, very good reading. It is also worthwhile to expand into light artillery as it appears to be the trend lately. After all, the cannon is just overgrown rifle.

    Since I am aware of similar weapons made By Skoda, this being 3,7cm KPUV vz.34, I am adding information source in English for this interesting alternative to presented Bofors gun. http://en.wikipedia.org/wiki/3,7cm_KP%C3%9AV_vz._34

    They are similar in terms of parameters, performance and features, but not same. Just to take a snapshot; 30deg inclined RHA of 3cm thickness would get penetrated at 500m range by this gun. The shells were in range of .80-.85 kg in weight, launched between 690-750 m/s muzzle velocity.

    • BTW: Do you know why almost all small cannons have 37mm caliber? I can tracked down to 37mm Hotchkiss naval gun, but not more – so why the Hotchkiss was 37mm? Not 36mm or 38mm but 37mm?

      • I think it has something to do with the minimum size for a explosive shell, some convention banned exploding small arms ammo if i remember correctly. (not sure how 20 mm variants figure in, maybe the convention was from a different era.)

        • According to Chinn (Machine Gun, Vol. 1), a treaty signed in 1870 prohibited explosive projectiles less than one inch in diameter (25mm). This was apparently due to the use of .58 caliber explosive bullets (Minie balls with a “tube” bore into the nose filled with black powder and topped by a pellet of fulminate) in the American Civil War.

          Benjamin Berkeley Hotchkiss began making rotary-barrel cannon in Europe about that time, mainly as naval secondary weapons to defend capital ships against the new “torpedo boats”, which were basically what we would later know as “sub chasers”, except with steam engines instead of Diesels and armed with the new Whitehead “locomotive torpedo”. (BTW, destroyers were originally called “torpedo boat destroyers”, as they were intended to act as escorts to protect fleet formations against the same attacker.)

          Hotchkiss, by experiment, concluded that a one and a half inch diameter projectile was the smallest size that could carry both a reasonably safe and effective impact/graze fuze and a worthwhile explosive filling. (Blackpowder at the time; the HE of the era was still too shock-sensitive to be used as a shell filling.)

          Put simply, pretty much everyone from then on followed Hotchkiss’ lead. It was the Maxim 37mm “pom-pom” that really put the “37” on the map, as it showed in WW1 that it was an effective light anti-aircraft weapon for use against strafers.

          At the same time, the French had already developed a light 37mm “infantry cannon” for shooting up machine-gun nests in the enemy trench lines. It was on a tripod, not a wheeled mount. And toward the end of the war they developed slightly heavier version with a solid shot intended for shooting up the early tanks. (Their Renault FT17 light tank used a similar gun firing HE shell for dealing with pillboxes.)

          It wasn’t until the early interwar period (1920s) that explosives chemistry and fuze technology had progressed enough to make an explosive round much below 35mm a paying proposition in terms of yield at impact and, especially, safety in transit and storage.

          This was why, besides the 37mm, there were so many oddball autocannon calibers in the years leading up to WW2. Notably 25mm, or one inch, which the IJN used as their standard light AA in triple mounts; it was actually a license-built copy of an experimental French Hotchkiss aircraft cannon. Their license agreement in 1935 stated that they were not to use it in aircraft, which suited the IJN fine as it was just a bit heavy for the horsepower of their available radial aero engines, like the Nakajima Sakae in the Mitsubishi “Zero” that was even then under development.

          The U.S. and UK experimented with .90 caliber machine cannon. The Russians took notice of this, and adopted several license-built designs in the metric equivalent, 23mm, which is still a standard bore over there today.

          30mm was the bore preferred by the Germans for aircraft cannon (with 20mm used in applications where there wasn’t enough room for a “thirty”), but for light triple-A they stuck to the old reliable 37mm bore.

          Oh, BTW, that treaty prohibiting explosive rounds under 25mm is still “in force”. It’s just that no nation that signed it has bothered to take any notice of it for the last ninety years or so.

          (No, the U.S. was not one of the signatories.)

          cheers

          eon

          • I salute your knowledge “eon”. I would not have known the reason for 37mm as asked by Daweo.

          • The somewhat odd calibers also derive from the old projectile weight based classification of artillery pieces:

            1½ pounder = 37mm
            3 pounder = 47mm
            6 pounder = 57mm
            12 pounder = 3″ = 76.2mm

            The British army still used this system partially up to late 1940s, but the regularity had already broken down, because for example the WW1 18 pounder field gun and post-WW2 20 pounder tank gun were both 84mm. The 20 pounder was, as far as I know, the last gun introduced to use that system, although the WW2 vintage 25 pounder (88mm) gun-howitzer remained in service longer than the 20 pounder tank gun.

  5. Thanx Ian…That is COOL!!! Nice to see such a ‘period piece’ so well preserved and in shootable condition…Thanks to the owner for spending that enormous amount of money on each round (a destructive device @$200 a pop)…did you guys ever hit the safe???

    CB in FL

      • I noticed that also – glad someone asked the question. Regarding the 37mm AT guns – interesting how the AT technology was so ‘behind’ in its development – by the time the 37mm was fielded it was well on its way to obsolescence as armor was rapidly becoming harder – beyond mere face or surface hardening…the Pak35/36 became known as ‘Hitler’s doorknocker’. Tamiya made a nice kit of both it and the 75mm AT gun…built ’em both in the 70s.

        CB in FL

        • The 37mm AT guns were 1930s designs and quite adequate at the time of their introduction. Armies did not want to introduce too big & heavy AT guns just to prepare for future developments, since moving the guns into position and even changing local positions were done by manpower alone. The prime example of that thinking was the French 25mm Mle.1937, which was significantly lighter than the 37mm guns. Unfortunately its armor penetration capability was only about the same as the 20mm Lahti and Solothurn S18-1000 anti-tank rifles…

          Still, there were larger caliber AT guns even at the beginning of the war. Especially the French and Czech 47mm AT guns were significantly more powerful than the 37mm guns*. The Soviet 45mm was only slightly so. As an early 1930s design the Austrian and later Italian 47mm Böhler was the weakest of them, although it still matched the Bofors 37mm gun in armor penetration (and bested the German PaK 35/36) and fired a much more useful HE shell.

          * Unfortunately for the French, they did not have nearly enough of the excellent 47mm APX AT guns in May 1940. They relied mostly on the obsolescent 25mm AT guns and 75mm field guns pushed to AT service.

    • @MacDemere:
      It’s actually HOHO and it’s simply for the fun of it, no connection with manufacturer.

      @Ian
      And one pointer – those pillows on the trails you were mentioning were not to SIT on them, but to LAY upon them: take a look at the actual photos of the Bofors gun in Polish service beneath that article (it’s in Polish, so of no use to most readers here anyway): http://www.dobroni.pl/rekonstrukcje,armata-przeciwpancerna-bofors-wz-36-kal-37-mm,6174
      The shield was way too low to cover a sitting man.

  6. Thankfully most burglars don’t open safes and ATM’s with artillery. Think of what would happen to all the money!

    What would happen if one were to use a Japanese Type 88 75 mm AA gun on the safe or a decommissioned SWAT team armored vehicle?

    • What would happen? In general fun would happen. Specifically, it depends on the thickness of the safe, location of hit etc…

      • A 20mm would do for most such “applications”. See the Clint Eastwood movie Thunderbolt and Lightfoot; the effects of the 20mm Oerlikon shown are just about right in terms of armor defeating capability, etc.

        Although I’d have expected a bit more back-fragmentation when firing that close to the “target”.

        An M9 rifle grenade would have probably done as well, but there would be the danger of the “jet” igniting the contents, etc.

        And of course, in one episode of “Hawaii Five-O”, a gang hijacked a load of traveler’s checks in CA (to unload in HI) by shooting up a bank armored car with a 2.36in rocket launcher M1, aka the WW2 “Bazooka”.

        Talk about overkill.

        cheers

        eon

    • In 1965 in New York a 20mm Lahti was used to shoot open a safe at a Brinks facility in about 2 hours. One of the accomplices turned in the others. It seems like Ian has a video interview with a machine gun collector who was active back then, who said the Feds took an interest in who had been buying anti-tank guns after that incident.

      Practically speaking, a thermal lance would have been faster and quieter. Against a safe it has to be seen as a novelty.

  7. Armored vehicles, 20 or 37mm cannon shot & correct placement strike, etc., Sounds like to “TV” work. Just route the Armored truck to appropriate shop & get to Plasma Cutting.

Leave a Reply

Your email address will not be published.


*