P-3 Orion

The Lockheed P-3 Orion is a four-engined, 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; it is easily distinguished from the Electra by its distinctive tail stinger or "MAD" boom, used for the magnetic anomaly detection of submarines.

Over the years, the P-3 has seen numerous design developments, most notably in its electronics packages. Numerous navies and air forces around the world continue to use the type primarily for maritime patrol, reconnaissance, anti-surface warfare and anti-submarine warfare. A total of 757 P-3s have been built.

Source: Wikipedia