Not sure if I understand your meaning by that. It is based on national standard GJB (National Military Standard).
The standard is something like A/BC-12 for many weapon systems (gun, missile, rifle etc.) The A is prefix for branch (Naval, Ground or Air) and can be omitted. B is the weapon's main category. The number is type which can by based on year of certification as in tank, artillery and rifle or something else in case of naval guns.
P: Any artillery (Gun, Howitzer or CIWS). The reason of "same denomination" is that they are all artillery.
J: Ship-borne.
11: 11 barrels? Another example of my uncertainty is H/PJ-38 the 130mm naval gun.