In most cases the crew in the back seat is the WSO (pronounced wizz-oh) which stands for Weapon Systems Officer. On older aircraft they operate complex avionics like bombing and navigation radars (A-6 Intruder, F-111 Aardvark, F-15E Strike Eagle) or long-range air-to-air radars (F-14 Tomcat), or offensive electronic countermeasures (EA-6 Prowler, F/A-18G Prowler, EF-111 "Sparky Vark"). On newer aircraft like the F/A-18F Super Hornet they're there to ease the workload on the pilot (who might operate them alone on single-seat models) and act as a second pair of eyes during combat. They rarely have duplicate flight controls even if their two-seat airframe began life as a trainer (like the F-15E and F/A-18F). And, of course, on large aircraft the second crew there to support the captain on take off and landing and to provide relief on long flights.



The models I named are obvious American-centric, but it holds true across models from other nations.