Navy NFO's can go to one of several aircraft (all of whose jobs are slightly different)
The Mighty P-3 Orion- 2 NFO on Crew one Tactical Control Officer and one Navigator/Communicator
EP-3 Aries II- basically the same plane as the P-3 just slightly different in jobs
E-2C Hawkeye- 3 NFO on Crew, mostly Airborne Early Warning job
F-14 Tomcat- 1 NFO on Crew, Radar Intercept Officer
F-18 Super Hornet- 1 NFO on Crew
S-3 Viking- usually 1 NFO on Crew but can have 2, WSO
the S-3 is in the process of being phased out, but they are currently sending NFO's to the Rag. Also the F-14 will be phased out sometime soon too. The P-3 community will be receiving a whole new airframe sometime in 2010 timeframe.
Lots of changes in the future as we move toward a joint service/ multi task type of airframe.