3 inch 20 cwt/77mm cases

[quote=“Tony Williams”]Nice story! :-D

I have my case listed as a Limbo but I have no evidence for that, someone must have told me - so it could be wrong. Certainly it is very much smaller than any case based on the 3" 20cwt/77mm would be: the rim diameter is only about 77mm.[/quote]


Do you know anything about the 3 inch 20 cwt or 77mm Naval guns? I joined the RN in 1959 and cannot recall having come across them. These cases are interesting in that they show the “parentage” of the A/S 10 cartridge.


The 3" 20cwt was a joint army/navy specialised AA gun developed (amazingly) even before WW1: it entered naval service in early 1914 in ‘Iron Duke’.

By the start of WW2 it was still the army’s main mobile AA gun, and wasn’t in fact declared obsolete until after the war. Large numbers of them also served in the RN during WW2 although in secondary roles, in destroyers (up to the ‘I’ class), minesweepers, auxiliaries and some DEMS.

The 77mm tank gun (its calibre was actually unchanged at 76.2mm) was developed during WW2 and was only ever fitted to the Comet tank, which emerged in 1944. It fired the same projectiles as the 17 pdr but the smaller cartridge case from the 3" 20cwt was used, so performance was not as good.

The pic below (from the Ammunition Photo Gallery on my website) shows the 77mm tank gun round (76x420R) next to the 17 pdr (76x583R).