The navy's designation system then:
first letter-role. F(fighter)P(Patrol)S(scout)T(torpedo)J(utility)N(t raining)R(transport)W(electronic warefare[radar,ELINT ect])O(observation)D(photo recce)
second letter-supplementary role or mission equipment( OS2U, SBD, TBM, ect)
first number - model
dash number- vairiant . So, for instance , in the Consolidated line of patrol planes we end up with PY, P1Y, P2Y(No bombing role), PBY, PB2Y,PB4Y, PB4Y-1. With loads of exceptions and ambiguity.( PBJ`s were always PBJ`s regardless of solid or glass nose fitiment. SNJ makes no sense at all...)
letter after dash number- modification of variant (F4U-1D) or role specific modification( F4F-5N, PB-1W)
Let alone the erraticly applied V(Heavier than air) or Z(Lighter than air letter) normally seen in unit designators(VF, VT, VP,VD) but also in type designators(Goodyear ZPG-1 patrol blimps) By the mid 1950s I expect the Navys designation system occupied a volume equivilent to the 1950-2012 Hong Kong phone books!
One can see why a new designation system was required in 1962!
Lots of potental for whatiferisims. Loads of fun!