The Lockheed SP-2H (P2V-7) was the last and most sophisticated derivative of the Neptune built for the Navy. First flown in early 1954, the SP-2H was the only production model to be equipped with underwing jet pods and the 'Jezebel' and 'Julie' submarine detection gear. The SP-2H saw considerable service in Operation Market Time during the Vietnam War, and some were used to drop electronic sensors along enemy truck routes.