Developed during the Cold War, the P-3's primary mission was to track Soviet Navy ballistic missile and fast attack submarines and to eliminate them in the event of full-scale war. At its height, the U.S. Navy's P-3 community consisted of twenty-four active duty "Fleet" patrol squadrons home based at air stations in the states of Florida and Hawaii as well as bases which formerly had P-3 operations in Maryland, Maine, and California. There were also thirteen Naval Reserve patrol squadrons identical to their active duty "Fleet" counterparts, said Reserve "Fleet" squadrons being based in Florida, Pennsylvania, Maryland, Michigan, Massachusetts (later relocated to Maine), Illinois, Tennessee, Louisiana, California and Washington. Two Fleet Replacement Squadrons (FRS), also called "RAG" squadrons (from the historic "Replacement Air Group" nomenclature) were located in California and Florida. The since-deactivated squadron in California provided P-3 training for the Pacific Fleet, while the squadron in Florida performed the task for the Atlantic Fleet. These squadrons were also augmented by a test and evaluation squadron in Maryland, two additional test and evaluation units that were part of an air development center in Pennsylvania and a test center in California, an oceanographic development squadron in Maryland, and two active duty "special projects" units in Texas and Hawaii, the latter being slightly smaller than a typical squadron.
Reconnaissance missions in international waters led to occasions where Soviet fighters would "bump" a P-3, either operated by the U.S. Navy or other operators such as the Royal Norwegian Air Force. On 1 April 2001, a midair collision between a United States Navy EP-3E ARIES II signals surveillance aircraft and a People's Liberation Army Navy (PLAN) J-8II jet fighter-interceptor resulted in an international dispute between the U.S. and the People's Republic of China (PRC) called the Hainan Island incident.
More than 40 combatant and noncombatant P-3 variants have demonstrated the rugged reliability displayed by the platform flying 12-hour plus missions 200 ft (61 m) over salt water while maintaining an excellent safety record. Versions have been developed for the National Oceanic and Atmospheric Administration (NOAA) for research and hurricane hunting/hurricane wall busting, for the U.S. Customs Service (now U.S. Customs and Border Protection) for drug interdiction and aerial surveillance mission with a rotodome adapted from the Grumman E-2 Hawkeye or an AN/APG-66 radar adapted from the General Dynamics F-16 Fighting Falcon, and for NASA for research and development.
The U.S. Navy remains the largest P-3 operator, currently distributed between a single fleet replacement (i.e., "training") patrol squadron in Florida(VP-30), 12 active duty patrol squadrons distributed between bases in Florida, Washington and Hawaii, two Navy Reserve patrol squadrons in Florida and Washington, one active duty special projects patrol squadron (VPU-2) in Hawaii, and two active duty test and evaluation squadrons. One additional active duty fleet reconnaissance squadron (VQ-1) operates the EP-3 Aries signals intelligence (SIGINT) variant at Naval Air Station Whidbey Island, Washington.
In January 2011, the U.S. Navy revealed that P-3s have been used to hunt down "third generation" narco subs. This is significant because as recently as July 2009, fully submersible submarines have been used in smuggling operations.
In October 1962, P-3A aircraft flew several blockade patrols in the vicinity of Cuba. Having just recently joined the operational Fleet earlier that year, this was the first employment of the P-3 in a real world "near conflict" situation.
Beginning in 1964, forward deployed P-3 aircraft began flying a variety of missions under Operation Market Time from bases in the Philippines and Vietnam. The primary focus of these coastal patrols was to stem the supply of materials to the Viet Cong by sea, although several of these missions also became overland "feet dry" sorties. During one such mission, a small caliber artillery shell passed through a P-3 without rendering it mission incapable. During another overland mission, it is rumored, but not confirmed, that a P-3 shot down a North Vietnamese MiG with Zuni missiles. The only confirmed combat loss of a P-3 also occurred during Operation Market Time. In April 1968, a U.S. Navy P-3B of Patrol Squadron 26 (VP-26) was downed by anti-aircraft artillery (AAA) fire in the Gulf of Thailand with the loss of the entire crew. Two months earlier, in February 1968, another one of VP-26's P-3B aircraft was operating in the same vicinity when it crashed with the loss of the entire crew. Originally attributed to an aircraft mishap at low altitude, later conjecture is that this aircraft may have also fallen victim to AAA fire from the same source as the April incident.
Lockheed produced the P-3F variant of the P-3 Orion, for Iran. Six examples were delivered to the former-Imperial Iranian Air Force (IIAF) in 1975 and 1976.
Following the Iranian Revolution in 1979, the Orions continued in service, after the IIAF was renamed the Islamic Republic of Iran Air Force (IRIAF). They were used in the Tanker War phase of the Iran-Iraq War and were operated by one of the most successful squadrons of the IRIAF during that conflict. A total of four P-3Fs remain in service.
On 2 August 1990, Iraq invaded Kuwait and was poised to strike Saudi Arabia. Within 48 hours of the initial invasion, U.S. Navy P-3C aircraft were among the first American forces to arrive in the area. One was a modified platform with a prototype system known as "Outlaw Hunter." Undergoing trials in the Pacific after being developed by the Navy’s Space & Naval Warfare Systems Command (SPAWAR), "Outlaw Hunter" was testing a specialized over-the-horizon targeting (OTH-T) system package when it responded. Within hours of the start of the coalition air campaign, "Outlaw Hunter" detected a large number of Iraqi patrol boats and naval vessels attempting to move from Basra and Umm Qasr to Iranian waters. "Outlaw Hunter" vectored in strike elements which attacked the flotilla near Bubiyan Island destroying 11 vessels and damaging scores more. During Desert Shield, a P-3 using infrared imaging detected a ship with Iraqi markings beneath freshly-painted bogus Egyptian markings trying to avoid detection. Several days before the 7 January 1991 commencement of Operation Desert Storm, a P-3C equipped with an APS-137 Inverse Synthetic Aperture Radar (ISAR) conducted coastal surveillance along Iraq and Kuwait to provide pre-strike reconnaissance on enemy military installations. A total of 55 of the 108 Iraqi vessels destroyed during the conflict were targeted by P-3C aircraft.
The P-3 Orion's mission expanded in the late 1990s and early 2000s to include battlespace surveillance both at sea and over land. The long range and long loiter time of the P-3 Orion have proved to be an invaluable asset during Operation Iraqi Freedom and Operation Enduring Freedom. It can instantaneously provide information about the battlespace it can see to ground troops, particularly the U.S. Marines.
Although the P-3 is a Maritime Patrol Aircraft, armament and sensor upgrades in the Anti-surface Warfare Improvement Program (AIP) have made it suitable for sustained combat air support over land. Since the start of the current war in Afghanistan, U.S. Navy P-3 aircraft have been operating from Kandahar in that role. Royal Australian Air Force AP-3C Orions operated out of Minhad Air Base in the UAE from 2003 until their withdrawal in November 2012. During the period 2008–2012, the AP-3C Orions conducted overland intelligence, surveillance and reconnaissance tasks in support of coalition troops throughout Afghanistan.
Recently, the United States Geological Survey used the Orion to survey parts of southern and eastern Afghanistan for lithium, copper, and other mineral deposits.
Three P-3C Orions, delivered to the Pakistan Navy in 1996 and 1997 were operated extensively during the Kargil conflict. After the crash of one, the type was grounded due to the loss of an entire crew; nonetheless, the aircraft were maintained in an armed state and airworthy condition throughout the escalation period of 2001 and 2002. In 2007, they were used by the navy to conduct signals intelligence, airborne and bombing operations in a Swat offensive and Operation Rah-e-Nijat. Precision and strategic bombing missions were carried out by the Orions, and in 2007, intelligence management operations were conducted against Taliban and al-Qaeda operatives.
On 22 May 2011, two out of the four Pakistani P-3Cs were destroyed in an attack on PNS Mehran, a Pakistani Naval station in Karachi. The Pakistani fleet had been readily used in overland, counter-insurgency operations. In June 2011, the U.S. agreed to replace the destroyed aircraft with two new ones, with delivery to follow later. In February 2012, the U.S. delivered two, additional P-3C Orion aircraft to the Pakistan Navy.
The Spanish Air Force deployed P-3s to assist the international effort against piracy in Somalia. On 29 October 2008, a Spanish P-3 aircraft patrolling the coast of Somalia reacted to a distress call from an oil tanker in the Gulf of Aden. To deter the pirates, the aircraft flew over the pirates three times as they attempted to board the tanker, dropping a smoke bomb on each pass. After the third pass, the attacking pirate boats broke off their attack. Later, on 29 March 2009, the same P-3 pursued the assailants of the German navy tanker Spessart (A1442), resulting in the capture of the pirates. In April 2011, the Portuguese Air Force also contributed to Operation Ocean Shield by sending a P-3C which had early success when on its fifth mission detected a pirate whaler with two attack skiffs.
Several U.S. Navy P-3C Orions, and two Canadian CP-140 Auroras, a variant of the Orion, have participated in maritime surveillance missions over Libyan waters in the framework of enforcement of the 2011 no-fly zone over Libya.
A U.S. Navy P-3C Orion supporting Operation Odyssey Dawn engaged the Libyan coast guard vessel Vittoria on 28 March 2011 after the vessel and two smaller craft fired on merchant ships in the port of Misrata, Libya. The Orion fired AGM-65 Maverick missiles on Vittoria, which was subsequently beached.
Several P-3 aircraft have been N-registered and are operated by civilian agencies. The US Customs and Border Protection has a number of P-3A and P-3B aircraft that are used for aircraft intercept and maritime patrol. NOAA operates two WP-3D variants specially modified for hurricane research. One P-3B, N426NA, is used by National Aeronautics and Space Administration (NASA) as an Earth science research platform, primarily for the NASA Science Mission Directorate's Airborne Science Program. It is based at Goddard Space Flight Center's Wallops Flight Facility, Virginia.
Aero Union, Inc. operated eight ex-USN P-3A aircraft configured as air tankers, which were leased to the U.S. Forest Service, the California Department of Forestry and Fire Protection and other agencies for firefighting use. Several of these aircraft were involved in the U.S. Forest Service airtanker scandal but have not been involved in any catastrophic aircraft mishaps. Aero Union has since gone bankrupt, and their P-3s have been put up for auction.