There are surely people on PPRuNe who know much more about this, but off the top of my head, until somewhat after WW2, the Navy had a completely different scheme of numbering aircraft from that used by the Army (Air Corps / Air Force).
Air Corps pursuits / fighters would be in the P-xx series. ie: P-40, P-47, P-47, P-80.
Air Corps bombers were B, as mentioned before.....
Navy fighters would be F[number][letter for manufacturer][number for variant if any]
ie: F4F would be a Grumman fighter, as would a later one, F6F General Motors built F4s during WW2 named the FM-1.
The P-80 became the F-80 after "unification" of the services in the late 1940s.
The PB series were Navy patrol/bombers. PBY would be a patrol bomber built by Consolidated. The PB4Y would be a later model. Examples of Martin patrol planes would be the PBM , etc.
etc etc