There is a decent chance you have already flown on one of the U.S. Navy’s key new aircraft—or rather, the 737 airliner it is based on. The P-8A Poseidon maritime patrol plane may not be as sexy as an F-35 stealth fighter, but in some ways it is far closer to the forefront of international flashpoints in the Pacific Ocean. Maritime patrol planes are essential for tracking the movement of ships and especially submarines across vast oceanic waters—and potentially sinking them in the event of hostilities.
Hunting submarines from the air, however, is an airpower-intensive job that requires numerous airframes spending thousands of flight hours flying long-distance patrol patterns over the ocean. Since 1962, the U.S. Navy has operated the P-3 Orion patrol plane, based on the four-engine L-88 Electra airliner. The turboprop-powered aircraft could spend a dozen hours flying low over the ocean to drop sonar buoys, scan the water for metallic hulls of submarines with its Magnetic Anomaly Detector (MAD) and potentially launch torpedoes. After fifty-five years of able service, however, the P-3s have accumulated thousands of service hours and their hulls are growing fatigued.
In 2004 the U.S. Navy selected the jet-powered Boeing P-8 Poseidon to succeed the aging P-3. Development proceeded relatively smoothly, in part due to the use of a preexisting airframe and the decision to phase in the P-8’s advanced systems in a series of increments rather than delivering them all at once. This led the P-8 unit costs to actually come in under budget, at $150 million per aircraft.
The P-8 is based on the 737-800ERX short-to-medium-range airliner. It typically has a flight crew of three and boosts stronger power generators for its onboard electronics. The Poseidon reportedly offers a much smoother ride than the Orion, thanks to its broader-swept wings and flight computers. Orion crews were often nauseated by the strong turbulence their low-altitude flight operations required.
While the P-8 does have a strengthened hull to operate at low altitude—though at reduced fuel efficiency compared to the P-3—it’s designed to perform most of its operation from high altitude, where the thinner atmosphere allows for greater fuel efficiency and a better vantage for some of its sensors. A Poseidon can loiter overhead at speeds as low as two hundred miles per hour, and can stay on station for extended times due to its in-flight refueling capability. However, with a maximum speed of 564 miles per hour, it can also dash two hundred miles per hour faster than the P-3 aircraft it is replacing.
The Poseidon’s primary payload is its diverse array of sensors. These include an APY-10 multi-mode synthetic aperture radar, which not only can track the position of ships over hundreds of miles away, but possesses a high-resolution mode which can spot submarine periscopes poking above the waves and even identify different classes of ships. An MX-20 electro-optical/infrared turret provides a shorter-range search option, while an ALQ-240 Electronic Support Measure (ESM) derived from a system onboard the EA-18G Growler functions as an electromagnetic sensor, particularly useful in tracking the positions of radar emitters.
A recent addition is the Advanced Airborne Sensor, a dual-sided AESA radar that can offer 360-degree scanning on targets on land or coastal areas, and which has potential applications as a jamming or even cyberwarfare platform.
A number of key systems on the P-8 are designed to track submerged submarines. A rotary launcher system in the rear of the P-8 can dispense sonar buoys into the water. A recent upgrade allows P-8s to employ new Multistatic Active Coherent buoys that generate multiple sonar pulses over time, allowing for greater endurance and search range. The P-8 also has its own acoustic sensor, and even a new hydrocarbon sensor that can “sniff” for fuel vapor from submarines.
However, the P-8 lacks the tail-mounted MAD sensor of the P-3 Orion, useful for detecting the metallic hulls of submarines while flying at low altitude. Various reasons have been offered for its removal: the MAD weighed too much at 3,500 pounds, it did not fit with the high-altitude search profile of the P-8, or the new sensors on the P-8 rendered it unnecessary. However, the U.S. Navy is reportedly developing a variant of the an air launched drone, called the High-Altitude Unmanned Targeting Air System, which can carry a MAD sensor  and transmit its findings back up to the P-8.
Five operator stations on the port side of the plane carry multifunction displays that can be configured to display whatever sensors and controls are most useful under the circumstances. The P-8’s computers are designed to fuse the data into a single coherent picture for the operators—and can then “push” that data to friendly ships and airplanes. This is a capability the U.S. Air Force has been struggling to integrate  into its new E-3G radar planes. The P-3 is also designed to be especially compatible with Navy RQ-4N drones.
In the event of hostilities, the Poseidon can carry five missiles, depth charges or torpedoes in a rotary launcher in the rear hull, and six more on underwing racks. While the P-3 had to fly low to deploy its torpedoes, the P-8 can use a special High Altitude Air Launch Accessory to transform its Mark 54 324-millimeter lightweight torpedoes into GPS-guided glide bombs that can be dropped from altitudes as high as thirty thousand feet. These shed their wings upon hitting the water and hone in on targets using onboard sonar. Poseidons can also carry Harpoon AGM-184H/K antiship missiles with a range of 150 miles.
Some argue  that the Poseidon could be turned into a sort of cut-rate B-52 bomber by fitting it with a variety of guided weapons, such as the AGM-158 long-range antiradar missile, the LR-ASM antiship missile or Small Diameter Bombs for precision ground attacks. Whether the Navy will choose to lean on the Poseidon’s multirole capabilities, or keep it focused on the antiship and surface ship mission, remains to be seen.
Flying Maritime Flashpoint
The Poseidon entered service with the U.S. Navy’s VP-16 squadron at Kadena Air Base on Okinawa in 2013, and around fifty out of a planned 117 are now operational in U.S. service.
The type’s patrol duties have placed it at the forefront of political disputes between the United States, China and Russia.
It was already a long-established and accepted custom for countries to intercept each other’s patrol planes over international airspace. However, this becomes risky when intercepting fighters perform unsafe maneuvers as part of their efforts to intimidate the observation planes. Such antics led to a collision between a Chinese fighter and an EP-3 observation plane in 2002 with fatal results for the Chinese pilot.
On August 19, 2014, a Chinese J-11 fighter flew within thirty feet of a P-8 flying more than 130 miles east of Hainan Island—even performing a barrel role over the forty-meter-long plane’s nose. This caused yet another in a long history of diplomatic spats between Washington and Beijing over the interception of the former’s observation aircraft.
At the root of the problem is that Beijing lays claim to broad swathes of the South China Sea that are considered international waters by most of the rest of the world. The United States maintains its right to fly over these waters, and refuses to cease its patrols. Chinese ships have been constructing artificial islands in recent years in an effort to reinforce their claims to certain areas, which the U.S. aircraft persist in monitoring.
You can see and hear the confrontation between the Chinese Navy and a P-8 crew observing one of the artificial islands in the video below:
Beijing has grown even more irate  since the United States reached an agreement with Singapore in December 2015 allowing P-8 aircraft to be based in the island city-state.
P-8s are also tangling with the Russian military. On May 9, 2017, a Russian Su-27 fighter buzzed within twenty feet of a Poseidon that was patrolling the Black Sea. The P-8s in turn have practiced chasing Russian submarines. According to the Aviationist , in December 2016 Poseidons were engaged in hunting one or two carrier-hunting Oscar-class submarines  in the Mediterranean. Maritime patrol aircraft are one of the few weapon systems that can routinely practice hunting their adversaries under operational conditions—stopping just short of releasing weapons, of course.
Given the centrality of the maritime patrol mission in current international disputes in the Pacific, the Persian Gulf, and (to a lesser extent) the Baltic, the P-8 has attracted significant international orders. India already operates eight P-8Is from Rajali Naval Air Station in Tamil Nadu State. These are modified with a MAD sensor in a tail stinger, as well as an extra APS-143 radar. Four more are on order for delivery by 2020.
The P-8 also has been a hit with Commonwealth countries. Australia has begun receiving the first of twelve to fifteen P-8As to replace its AP-3C patrol planes. The United Kingdom has nine P-8s on order, and New Zealand announced this month that it approved the purchase of four Poseidons for $1.46 billion. Further afield, at least three P-8s appear to be part of a new $110 billion arms deal with Saudi Arabia, and Norway has five coming its way as well. Other countries reportedly considering the patrol plane include Canada, South Korea and Turkey.
As trans-Pacific relations assume new prominence in the twenty-first century, the P-8 will remain one of a number of means by which the United States and other operators assert their presence over international waters. In the event of conflict, they would also serve a vital role hunting down marauding submarines and tracking the movements of surface adversaries. These qualities explain why the docile-looking patrol plane is in such heavy demand around the world.
Sébastien Roblin holds a master’s degree in conflict resolution from Georgetown University and served as a university instructor for the Peace Corps in China. He has also worked in education, editing and refugee resettlement in France and the United States. He currently writes on security and military history for War Is Boring .