Bofors L/60 Mark 2 (40 mm)

The 40 mm Bofors L/60 Mark 2 on USS Phelps (DD-360).

Description

The Bofors L/60 Mark 2 is a naval anti-aircraft quad mounting that consists of four water-cooled, US-produced Bofors 40 mm L/60 guns. The Bofors 40 mm L/60, also known as the "Bofors L/60", the "Bofors gun", or simply "the Bofors", was a highly successful Swedish anti-aircraft gun design of the interwar period and was widely used during the Second World War by both sides and in all theatres and remained in service long after the end of WWII.

Other variants of the Bofors 40 mm gun within the game include:

• Bofors L/60 Mark 1: US-produced, water-cooled twin mount
• Bofors L/60 Mark 3: US-produced single mount
• 4 cm Bofors Flak 28: German captured single mount
• QF Mark V: British-produced, water-cooled twin mount
• QF Mark VII: British-produced single mount
• QF STAAG Mark II: British-produced, water-cooled twin mount with onboard radar and fire control systems
• Bofors (40 mm): Army version, mounted on various US, British, and French anti-aircraft vehicles (SPAA)
• MEL58: Bofors 40 mm L/70 (increased barrel length and rate of fire), mounted on Jaguar
• M266: Army version Bofors 40 mm L/70 (increased barrel length and rate of fire), mounted on M247

Vehicles equipped with this weapon

• USS Phelps
• USS Sumner
• HMS Arethusa
• USS Helena

General info

The Bofors L/60 Mark 2 has a barrel diameter of 40 mm and has a barrel length of 2.25 m. It has a magazine size of 4 rounds per gun and has a rate of fire of 156 rounds per minute, though firing for too long will jam the gun.

Available ammunition

Depending on the vehicle, there are up to three belts available. Note that Default and Universal refer to the same belt, depending on the vehicle.

• Default/Universal: AP-T/HEFI-T
• 40 mm HE clips: HEFI-T/HEFI-T/HEFI-T/AP-T
• 40 mm AP clips: AP-T/AP-T/AP-T/HEFI-T

Not all belts listed are available on all vehicles equipped with this weapon.

Penetration Statistics
Ammunition	Penetration @ 0° Angle of Attack (mm)
	10 m	100 m	500 m	1,000 m	1,500 m	2,000 m
HEF-I	_	_	_	_	_	_
AP-T	80	77	66	57	50	45

Shell Details
Ammunition	Projectile Mass (kg)	Velocity (m/s)	Explosive Type	Explosive Mass (kg)	TNT Equivalent (kg)	Fuse Delay (m)	Fuse Sensitivity (mm)	Normalization at 30°	Ricochet
									0%	50%	100%
HEF-I	0.9	881	Tetryl	0.068	0.0986	0.0	0.1	_°	_°	_°	_°
AP-T	0.882	874	N/A	N/A	N/A	N/A	N/A	_°	_°	_°	_°

Tetryl is equivalent to 1.45x TNT.

Comparison with analogues

All naval Bofors 40 mm L60 guns are virtually identical, the only difference between them being the rate of fire: all single mounts fire at 160 rpm, while twin and quadruple mounts fire at 156 rpm. They all fire the same ammunition from 4-round ammunition clips and have a short enough reload that they can sustain continuous fire as if there wasn't a reload at all. In other words, their cyclic rate of fire (mechanical rate of fire) is the same as their effective rate of fire (rate of fire with reload times taken into account). All naval Bofors 40 mm L60 guns can jam if fired for too long.

The only naval Bofors 40 mm L/70 gun currently present in the game is the MEL58, which is, by and large, superior with a much higher rate of fire of 240 rounds per minute. The only other difference is the HE round: the MEL58's HE round has less explosive mass (0.03625 kg TNT eq.), but it has a higher muzzle velocity (1030 m/s).

It should be noted that 4 cm Bofors Flak 28 is the only naval Bofors gun in-game with access to a pure HE ammunition choice, at the cost of not having any AP options. Every other naval Bofors gun has ammunition choices comprised of a mix of HE and AP, in ratios of 1:1, 3:1, or 1:3.

Compared to other common guns of similar calibre:

• 3,7 cm SK C/30 (37 mm): The 3,7 cm SK C/30 has a higher muzzle velocity for both its AP and HE rounds (1000 m/s) and has a stronger AP round (87 mm @ 10 m, 0°; 0.0374 kg TNT equivalence); but it has a much slower rate of fire (30 rpm), has a weaker HE round (0.0274 kg TNT equivalence), and has a lower projectile mass for both its AP round (0.82 kg) and HE round (0.75 kg). This gun is single-shot and cannot jam.

• 3,7 cm FlaK-Lafette C/36 (37 mm) and 3,7 cm FlaK-Lafette LM/42 (37 mm): These guns have a higher rate of fire (250 rpm), but they have a lower muzzle velocity for both their AP round (845 m/s) and HE round (815 m/s), have a weaker AP round (67 mm @ 10 m, 0°) and a weaker HE round (0.04403 kg TNT equivalent), and have a lower projectile mass for both their AP round (0.7 kg) and HE round (0.623 kg). These guns fire from a 5-round ammunition clip and have a very quick reload, so their cyclic rate of fire and effective rate of fire are practically identical. They cannot jam.

• 70-K (37 mm): The 70-K has a higher muzzle velocity for its HE round (880 m/s); but it has has a lower rate of fire (150 rpm), has a lower muzzle velocity for its AP round (880 m/s), has a weaker AP round (79 mm @ 10 m, 0°) and a weaker HE round ((0.05698 kg TNT equivalence), and has a lower projectile mass in both its AP round (0.758 kg) and HE round (0.72 kg). It fires from a 500-round magazine and can jam if fired for too long.

• 2pdr QF Mk.IIc (40 mm) and 2pdr QF Mk.VIII (40 mm): These guns have a higher rate of fire (200 rpm) and have a lower projectile mass in their AP round (0.91 kg); but they have a lower muzzle velocity for its AP and HE rounds (701 m/s), have a weaker AP round (60 mm @ 10 m, 0°) and a weaker HE round (0.071 kg TNT equivalence), and have a lower projectile mass in both their HE round (0.82 kg). They fire from a 56 round magazine and cannot jam.

Usage in battles

One of the best medium-range anti-aircraft cannons in the game, the Bofors L/60 Mark 2 provides very good AA coverage for any ships that it's mounted on. With a 0.0986 kg TNT equivalent explosive charge in each HE round, any hit on an enemy aircraft will usually result in critical damage, if not a kill. The rounds that these guns fire have an above-average muzzle velocity and projectile mass, resulting in a much further effective range than guns of a similar calibre: laterally (i.e. targeting surface targets), the maximum range is about 3.25 km.

Despite the guns' small magazine size of only four rounds, the reload is short enough that there isn't any noticeable difference between its cyclic rate of fire (the rate of fire only considering the mechanical speed of the gun) and its effective rate of fire (the rate of fire accounting for reload times). In other words, it can sustain virtually continuous fire, as if there was no reloading at all. However, this comes at the cost that if fired for too long, the gun can jam. For this reason, it can be advantageous to set the AI gunners to only target aircraft. If allowed to target surface targets, the AI gunners will often waste ammunition on targets well outside of the gun's maximum range, leaving the guns jammed when actually needed.

Since the Bofors L/60 Mark 3 is currently only mounted on destroyers and cruisers in-game, there is no reason to use any ammunition option other than 40 mm HE clips since it contains the highest ratio of HE to AP rounds. While the AP rounds do have a very gun penetration for its calibre, armoured targets are more effectively dealt with using the destroyer's main armament anyway. With the 40 mm HE clips, the Bofors L/60 Mark 3 will have the highest effectiveness against its intended targets: aircraft and small boats.

Pros and cons

Pros:

• Large explosive mass in HE round
• High-penetration AP round
• Very quick reload
• Large range

Cons:

• Can jam if fired for too long

History

In 1928, the Swedish Royal Navy contracted the Bofors Company to design a suitable replacement for their Vickers 2-pounder guns anti-aircraft guns (the Vickers "Pom-Poms"). Work on the design began right away and a prototype model was produced by mid-1930. The prototype had a vertical sliding breech block design and was automatic. Upon firing, the recoil of the gun would open the breach and eject the spent casing out its rear whilst an autoloading mechanism would insert the next round into the empty breach, after which the action of the gun sliding back into place would close the breach once again, leaving the gun ready to fire once more.

While proving the potential of the design, the prototype failed to meet the specified rate of fire requirement of 130 rounds per minute. It wasn't until 1934 that a production model, 40 mm L/60 Model 1934, was ready. In the following years, minor improvements led to the development of 40 mm L/60 Model 1936, which would finally be accepted into Swedish service as 40 mm/60 Model 1936. Despite its name, the barrel length of the 40 mm L/60 Model 1936 was actually 2250 mm (56.25 calibres).

Interest for the gun began in the United States in 1937 when the US Army purchased and tested a Model 1936. In 1939, York Safe and Lock Company employees were sent to Sweden for a demonstration of the gun. In 1940, the gun was demonstrated to the US Navy Bureau of Ordnance (BuOrd) by the Dutch frigate HNLMS Van Kinsbergen in the Caribbeans. Impressed by its capabilities, BuOrd purchased its own Model 1936 for further testing. With the approval of BuOrd, representatives of York Safe and Lock Co. were sent to Sweden to negotiate for and acquire the rights to the produce the gun in America. The license was eventually acquired on July 21, 1941, though limited production had illegally begun prior to this using British blueprints. Nevertheless, the designs acquired from Bofors Company had many problems that made them unfit for both mass production and use on USN warships.

There were several problems with the Model 1936 design that made it unacceptable for naval service. First, the original design was air-cooled, which limited its firing time; the gun in USN service would have to be water-cooled. Second, replacement of the barrel, which might have to be done in combat, was very time consuming; the barrel screw design was changed to an interrupted screw so that a 90° turn was enough to lock it in place. Third, the original gun was hand-trained and traversed too slowly; an electric drive was needed. Fourth, the fuses in the Swedish ammunition design were far too sensitive for conditions at sea; the much more precise Mark 27 fuse was developed as a replacement, and adopted by both the United States and Britain.

Next are the mass production problems, the first of which was that the original designs were written in Swedish, used metric units, and drawn using first-angle projection; all notes would need to be translated to English, all measurements to Imperial units, and all technical drawings to third-angle projections, the US industrial standard. Another issue was that the specified production methods for many of its parts were very inefficient; many parts originally made by hand would have to be redesigned to be done by automatic or semi-automatic machines. In addition, the dimensions of many parts on the blueprints were not the same as those from the finished product. This was because many parts were originally intended to be hand-fitted on final assembly, making every gun slightly different; to ensure total interchangeability of parts, all parts would have to be produced under such precise tolerances than they all fit together smoothly upon final assembly, eliminating any need for hand-fitting. Altogether, these problems would waste valuable materials, machine time, and man-hours, and because of the variability between each gun, field maintenance of the gun would be extremely difficult. The monumental task of fixing these mass production problems was given to York Safe and Lock Co. for the production of naval Bofors guns, and as a result, radical changes were made to the original design. Chrysler Corporation was contracted by the US Army for the production of army guns and coordinated with York to ensure that all measurements matched between naval and army versions.

Eventually, York Safe and Lock Co. fell out of the program. Production of both army and navy versions of the Bofors gun was then given to Chrysler Corporation: the Chrysler division produced the breach and recoil cylinder, the DeSoto division produced the breech casing, the Dodge division produced the loading tray, the Chrysler Hyland Park Plant produced the barrels and water jackets (two of each were produced for every gun), the Plymouth division produced the automatic loader and did final assembly of the gun, and over 2,000 subcontractors and other Chrysler plants produced miscellaneous parts. In addition to all previous changes, Chrysler further improved efficiency wherever they could. In the end, the changes to the design and production reduced the time to assemble a single gun from 450 hours to 11 hours and saved 7.5 million pounds of material and 1.9 million man-hours over just one year. Chrysler produced both single and twin guns for the US Navy.

The twin guns were essentially two mirrored single guns strapped together; the left and right guns were designated 40 mm/56 Mark 1 and Mark 2 respectively. The Mark 3 Quad mount used two twin guns mounted side-by-side with two crewmen seated one to the left of the left-hand pair and one to the right of the right-hand pair. The crewman on the right-hand side of the guns was the gun trainer; he trained the guns horizontally by turning a crank. The crewman on the left-hand side was the gun pointer; he elevated the guns in the same manner and also fired them by pressing a foot pedal. The guns could be toggled between single-fire and full-automatic modes with a switch on the pointer's side. In full-automatic mode, the guns could fire at around 120 rounds per minute. The mount was electrically driven and could train at a rate of 26°/s and could elevate at a rate of 24°/s between -15° and 90°. The mount could also be remotely controlled by a Mark 51 fire control system crewed by its own pointer and range setter. Behind the gun pointer and trainer was a platform on which stood the mount captain and four 1st loaders, one for each gun. In combat, a line of ammunition passers formed to pass ammunition from the storage along to the 1st loaders. Ammunition was produced in 4-round clips with both HE and AP clips, as well as self-destructing variants — set to explode between 4,000 and 5,000 yds. (3,700 - 4,570 m) — of both, being produced. Ammunition was loaded into the top of each gun into their ammunition trays. Spent casings were ejected out the rear of each gun and sent down chutes towards the front of the gun, where they were flung safely away from the crew. The guns of the Mark 2 Quad mount were water-cooled and had water jackets, the coolant tanks and pumps for which were located at the rear of the mount. Altogether, the Mark 2 Quad mount could weigh up to 23,800 lbs. (10,796 kg).

The Mark 1 Quad mount began production early 1942 and entered service in July 1942, mounted on the destroyer USS Coghlan (DD-606). The USN standard medium anti-aircraft gun at the time was the 1.1"/75 "Chicago Piano" gun was unreliable and largely inadequate as an AA gun. The Bofors gun was quickly adopted as the new standard medium AA gun and began to be mounted on virtually every ship in the US Navy. The United States also supplied Britain, the USSR, and several other nations with Bofors guns as part of the Lend-Lease policy. In 1945 though, the Bofors gun, too, was determined by the US Navy to be insufficient and development for a replacement, the 3"/50 gun, was started. However, the development was long and the replacement program was slow. As a result, the Bofors gun remained in well into the 1970s. Over the course of World War II, over 2,300 Mark 2 Quad mounts were produced.

Media

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  Bofors L/60 Mark 2, mounted on USS Sumner

See also

• Bofors L/60 Mark 1 (40 mm)
• Bofors L/60 Mark 3 (40 mm)

External links

• NavWeaps - USA Bofors 40 mm L/60 Model 1936
• York Blog - A Road Named N.O.P., Arsenal and Whiteford; Part 2 – Bofors at York Safe & Lock Co.
• allpar.com - Chrysler Corporation, Gun Maker: Bofors Guns of World War II
• Wikipedia - Bofors 40 mm gun