According to the NavWeaps.com website, the 40mm was "Probably the best automatic cannon anti-aircraft weapon of World War II, Bofors guns of this type remained in service long after the war ended. This weapon was used on almost every major USA and UK warship of World War II and was a very potent AA gun.  This weapon traces its roots back to a 1918 Krupp design - the Bofors Company was partly owned by German interests until 1930 - but the finished product was entirely a Bofors design owing little or nothing to Krupp influence. 

The US Navy had a good deal of pre-war interest in this weapon and BuOrd purchased a sample of an water-cooled twin version from Bofors in early 1940. Bofors instead sent an air-cooled version and this arrived in New York from Sweden on 28 August 1940. During the same month, the Dutch escort vessel van Kinsbergen demonstrated these weapons and their Hazemeyer control system to USN observers in a test off Trinidad. The observers were not impressed by the control system, but were favorably impressed by the guns themselves. 

It should be noted that the US Army and Navy considered the original Bofors Model 1936 design to be completely unsuitable for the mass production techniques required for the vast number of guns needed to equip the anti-aircraft batteries and ships of the US military.

US manufacturers made radical changes to the Swedish design in order to minimize these problems and as a result the guns and mountings produced in the USA bore little resemblance to their Swedish ancestors. For example, all but the earliest US guns were built to English measurement units rather than to metric units. To give one additional example of the design differences made for USA produced weapons; the Chrysler Corporation redesigned ten components to suit mass production techniques and this was claimed to have saved some 7,500,000 pounds (3,402,000 kg) of material and 1,896,750 man hours during a year's production, as well as freeing up 30 machine tools for the production of other components. 

The first USN pilot twin was completed in January 1942 and the first quad in April 1942. The first shipboard quad installation was on the gunnery-training ship (ex-battleship) USS Wyoming (AG-17) on 22 June 1942, and the first twin installation was on the destroyer USS Coghlan (DD-606) on 1 July 1942.

The USN 40 mm/56.3 Mark 1 and 40 mm/56.3 Mark 2 Bofors guns were both water-cooled and were used for all twin and quad mountings. The Mark 1 was a left-hand weapon while the Mark 2 was a right-hand weapon. Except for the barrel assemblies, the components were not interchangeable. These weapons could be fired in single-shot or automatic mode via a selector switch on the side of the slide. 

As mentioned, there are six mounts included included.  They come as one part, no assembly is required.  That will make them easier to install, but perhaps more difficult to paint. 

The detail and fineness of these weapons is excellent.  The shields are nice and thin, as are the barrels.  The rails around the back of the mount, and the gun sights are especially impressive.  The level of detail and the thinness of the parts is really remarkable. 

 This is Black Cat Models set AC700006b, 40mm Bofors Quad Gun Mk.2 Mod.3 (x6).  It retails for about $7.10 USD, and is available directly from Black Cat Models - who I'd like to thank for this review sample - or from some of our other fine sponsors.