British-made 75mm ammo for WW2 tank guns

[Tony Williams]

Does anyone know when the UK started to manufacture 75x350R ammo during WW2?

This was used in the guns in the US M3 tanks (Grant and Lee in British service) which were being delivered from late 1941/early 1942 and in the M4 (Sherman) which followed on. British-made 75mm guns, using compatible ammo, didn't enter production for the Cromwell and Churchill until 1943.

The reason I am asking is that Vickers were proposing to make a 75mm L/50 high-velocity tank gun early in 1942. This proved too big to fit into the Cromwell as planned, but the Comet was designed around it. The gun was later modified to use 76.2x420R ammo, an uploaded version of the old 3 inch 20 cwt AA gun cartridge, firing 17 pdr projectiles and redesignated 77mm.

Does anyone have any detail on the ammo for this Vickers 75mm L/50 High Velocity? Why was the 75mm calibre chosen, when it wasn't a British calibre (whereas 76.2mm certainly was)?

 

[Bonnex]

Tony,

Not my strong suit but I have a note from the Annual Report of the OB saying that in June 1943 it was decided not to manufacture 75mm in the UK. Of course changes of plan were frequent. Is there any evidence of UK manufacture?

 

[Tony Williams]

Many thanks, Norman, for sending me the info on the 75mm HV. This makes it clear that it was indeed based on the 3 inch 20 cwt case slightly necked down to take US 75 mm projectiles. However, I still don't understand why it was proposed to use US 75mm projectiles in the first place rather than British 76.2mm, especially if they weren't being made in the UK.