The PRR borrowed several NH EP-3s (box cab design) electrics for testing when the railroad designed the GG-1. The GG-1 was almost a carbon copy of the EP-3 except for the car body. The NH needed new freight power in the 1930s. This lead to the EF-3 (streamlined cab) design which was a copy of the GG-1s built by Westinghouse. Fifteen of the NH's EF-3s were converted to passenger service in 1944 by adding train heating boilers and some other modifications. These engines became EF-3bs. These engines were also used for heavy freight service. They were really dual service engines.
The NH also had another streamlined class - the EP-4 that looks almost identical to the EF-3. This was mostly used in passenger service. The most famous class that has been made Lionel, MTH and others is the EP-5 (jet) class.
The NH used E to designate an Electric engine. F was used to designate a freight engine and P used to designate a Passenger engine. Thus EF = Electric Freight engine.
NH Joe