U.S. 40mm Bofors Anti-Aircraft - WWII

40mm AA Round
The 40mm Bofors was arguably the most successful weapon of its type. The initial design was the result of a collaboration between the German firm Krupp and the Swedish company AB Bofors during the years immediately following WWI. In the 1930's the Swedes continued development on their own, producing the single barrel L/60 gun. It quickly became internationally recognized as a superior antiaircraft weapon and was widely used during the Second World War, adopted by many nations.

U.S. Army and Navy designers developed customized variants for their purposes.
The Navy developed a water-cooled design on a turntable in two gun (Mk.I) and four gun (Mk.II) variants. Introduced in 1942 they became the Navy's standard intermediate range anti-aircraft weapon and were extremely effective, remaining in service until the 1950's.
The Army made modifications to the L/60 keeping the air-cooled single barrel configuration, placing it on a wheeled gun carriage, shown here.
U.S. 40mm M1
(Image Re-Posted with Permission)

40mm Quad in Action
40mm Dual Mnt

U.S. Navy Mk.II (Quad) and Mk.I (Dual) Mounts
(The Quad is actually two modified Duals,
side by side on a single turntable.)

40mm Rounds

This is the MK-3 inert practice round made for the Navy, dated October 1942.

The MK-2 projectiles, dated 1945, are made of steel with large tracer elements. Aluminum nose caps held the fuze assemblies.

The weapon is clip fed, each clip holding four rounds.

The color codes identify the round type. As I understand it, the green bodies indicate High Explosive. 
From a 1944 Navy Handbook :
Blk/White/Red = HE-I-T (High Explosive-Incendiary-Tracer)
Yellow/Red     = HE-I-TDI-SD  High Explosive-Incendiary-Tracer,Dark Ignition-Self Destruct
The one with the black fuze is not described.
(Can anyone help identify?)

It is not clear if these projectiles are the original nose/body configurations.
Without the noses, they look identical. All the tracer elements appear to be designed to burn through initiating a Self Destruct.

U.S. Navy, 40mm Bofors

A close-up of clipped rounds in the magazine feed rollers.

Note the different round types.
Also the water hoses connected to the cooling jackets around the barrels.

There used to be a detailed history and data about the development of the Swedish Bofors 40mm on this website, but it seems to be a dead link now.
If anyone has a replacement to suggest, let me know.