Military surveillance aircraft
Boeing E-3 Sentry
Adaptation of the Boeing 707 jetliner as an airborne warning and control system (AWACS) aircraft capable of detecting low-flying intruders with its fuselage-mounted radar and providing battlefield communications and coordination. Out of production but used by the USAF and various other operators.
Lockheed P-3 Orion
Maritime patrol aircraft: derivative of the Lockheed Electra turboprop airliner. Out of production but still in use.