Ordnance QF 3.7in Mk III, is under development by Vickers partly as a private venture, firing trials to begin in 1936. It is based on a similar Naval AA gun.
In the past, the reasoning given for the adoption of the 3.7" gun on RN cruisers was that there was a desire for commonality between the Army and the Navy, and the Army already had the 3.7" gun in service.
I noticed RLBH had fitted a 3.7in gun on his cruisers since the 1929 so therefore I've reversed history and had the Army adpot a naval weapon for a change!
Same for the Pom-Pom mounted on a truck or small 4x4 vehicle like the Matador gun tractor.