3.7" aa

[Tony Williams]

Originally Posted by chrisgrove

Post war in UK, the 3.7 inch ordnance was used for the 32 pounder towed AT gun (and for the Tortoise).

Not quite. The ammo for the 3.7" AA and 32 pdr was different, so needed a different barrel to fit.

And of course there were two very different types of 3.7" AA - the Mk 6 was much bigger than the Mks 1-3 guns and used larger cartridge cases for a much higher velocity.

So there were three cartridges used in the same calibre, none of them interchangeable:

3.7" AA Mks 1-3: 94 x 675R with 135mm rim diameter (12.7 kg shell fired at 790 m/s)

3.7" AA Mk 6: 94 x 857R, rim 150mm (12.7 kg shell fired at 1,040 m/s)

32 pdr AT: 94 x 909R, rim 141mm (14.5 kg shot fired at 878 m/s).

See: http://quarryhs.co.uk/ammotable10.html