According to Wikipedia: "The Lockheed P-3 Orion is a four-engine turboprop anti-submarine and maritime surveillance aircraft developed for the United States Navy and introduced in the 1960s. Lockheed based it on the L-188 Electra commercial airliner. The aircraft is easily recognizable from the Electra by its distinctive tail stinger or "MAD Boom", used for the magnetic detection of submarines.
All Royal Australian Air Force P-3C/W aircraft which have been fully upgraded with totally new mission systems by L-3 Communications to include an Elta SAR/ISAR RADAR and a GD-Canada Acoustic Processor system."