While based on the same design philosophy as the Electra, the aircraft differed structurally it had 7 feet (2.1 m) less fuselage forward of the wings with an opening bomb bay, and a more pointed nose radome, a distinctive tail "stinger" for detection of submarines by MAD, wing hardpoints, and other internal, external, and airframe-production technique enhancements. The first flight of the aircraft's aerodynamic prototype, originally designated YP3V-1, took place on 19 August 1958. Lockheed modified the prototype YP3V-1/YP-3A, Bureau Number (BuNo) 148276 from the third Electra airframe c/n 1003. The first Orion prototype was a converted Lockheed Electra. In April 1958, Lockheed won the competition and was awarded an initial research-and-development contract in May. Lockheed suggested a military version of its L-188 Electra, then still in development and yet to fly. Modifying an existing aircraft should save on cost and to allow rapid introduction into the fleet. Navy called for proposals for replacement of the piston-engined Lockheed P2V Neptune (later redesignated P-2) and Martin P5M Marlin (later redesignated P-5) with a more advanced aircraft to conduct maritime patrol and antisubmarine warfare. 6 Notable events, accidents, and incidents.The Boeing P-8 Poseidon will eventually replace the U.S. In 2012, it joined the handful of military aircraft including the Boeing B-52 Stratofortress, Boeing KC-135 Stratotanker, Lockheed C-130 Hercules and the Lockheed U-2 that the United States military has been using for more than 50 years. Numerous navies and air forces around the world continue to use the P-3 Orion, primarily for maritime patrol, reconnaissance, anti-surface warfare and anti-submarine warfare. Over the years, the aircraft has seen numerous design developments, most notably in its electronics packages. The aircraft is easily distinguished from the Electra by its distinctive tail stinger or "MAD" boom, used for the magnetic anomaly detection (MAD) of submarines. Lockheed based it on the L-188 Electra commercial airliner. 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.