[quote=“TonyWilliams”]The 13.2mm Hotchkiss round was used in the Breda M31 HMG which was fitted to some light tanks and also (I believe) used by the Italian navy (I recall seeing a pic of some multiple mountings on submarines).
The Italian Air Force never used the 13.2mm cartridge (AFAIK the only aircraft which did were Swedish and Romanian); they used the 12.7x81 SR (Vickers export .5 inch) instead, in Breda-SAFAT and Scotti MGs.[/quote]
13,2x99 was mainly an Italian Navy ammunition and Breda 31 HMG was the backbone of short range AAA during the '30s, with the 40 mm Vickers and 37 mm Breda.
During this period this HMG was on of cruisers, destroyers, torpedo boats, submarines ad MAS but towards the end of '30s was replaced by Breda and Scotti 20 mm HMG, remaining practically only on submarines, MAS and auxiliary vessels.
Italian Army experimented the Breda 31 on CV tankettes during the '30s (five sold to Brazil in 1938) and installed this weapon only on Armoured Command Vehicles of self propelled artillery units (75/18, 75/34, 105/25) on M41 and M42 tank chassis.
These weapons used a 12 rounds magazine, specially designed for use in AFV.