Japan may be the only nation to have experienced having its economy truly crippled by submarine warfare. Yes, the costly campaigns waged by German U-Boats during World War I and II targeting the United Kingdom’s supply lines across the Atlantic are better known, but the U-Boats ultimately were defeated by Allied anti-submarine warfare . By contrast, Allied submarines sank 55 percent of Japan’s merchant shipping during World War II, crippling the circulatory system of a Japanese empire spread thinly across the Western Pacific.
That historical experience must be high on the Japanese Self Defense Force’s mind as it considers the rapid buildup of the Chinese PLA Navy submarine force, which will soon be the largest submarine operator on the planet with over seventy submarines operational. While most of these are shorter-range diesel and AIP-powered submarine, this is little consolation for Japan, which is easily within range and economically dependent on secure shipping lanes.
Large maritime patrol planes are a key platform in Anti-Submarine Warfare (ASW), and for over a half-century Japan has operated U.S.-built four-engine P-3C Orion turboprops, which spend long hours patrolling the seas and tracking the movements of vessels around Japanese waters—including any submarines they succeed in detecting. But as the Orion airplanes neared the end of their service lives, both Japan and the U.S. separately developed jet-powered successors.
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The U.S. P-8 Poseidon is derived from the twin-engine Boeing 737-800 airliner and is optimized for higher-altitude patrols. By contrast, the Kawasaki P-1, which first flew in 2007, is a clean-sheet four-engine design that can handle both low and high-altitude operations. (The P-1 was developed concurrently with an especially portly twin-engine Kawasaki C-2 transport, and shares about 25 percent of its weight in parts.)
Aerodynamically, the P-1’s broad, stubby wings allow for a lower stall speed and better low-altitude performance than the P-8. You can see a P-1 show surprising agility for a thirty-eight-meter long airplane with an eighty-eight-ton maximum takeoff weight at the 2018 Berlin Airshow in this video.
The Kawasaki design’s four F7-10 turbofans provide additional redundancy while on lengthy patrols and are designed to be ten decibels quieter than the P-3’s turboprops for acoustic stealth. A P-1, which has a maximum range of nearly five thousand miles, can transit to station over 30 percent faster than a P-3 at a sustainable speed of 518 miles per hour (or a maximum is of 621 mph), then assume a slow patrol pattern using just two engines to conserve fuel.
A crew of two pilots and nine mission specialists operate the jet and its sensors. The P-1 is also is the first operational aircraft ever to use a fiber-optic fly-by-wire system (fly-by-light), which in theory is more reliable and less likely to create electromagnetic interference with onboard sensors than the traditional kind.
The P-1’s extensive array of onboard sensors begin with no less than four powerful HPS-106 Active Electronically Scanned Array radar antennas providing 360-degree coverage around the plane. These can scan the surface for ships, even distinguishing between different types or picking up the protruding snorkels or sensor masts from submarines—but can also function in air search mode, allowing it to serve as an impromptu AWACS plane. There’s also an electromagnetic sensor antenna (or Electronic Support Measure) mounted on top of the cockpit that’s useful for spying on and locating enemy sensor and communication activity, and an HAQ-2 Infrared/Electrooptical sensor turret under the chin for scanning vessels.
To round out the package, an HQA-7 acoustic processing unit listens for the sound of submarine diesels and a Canadian-built ASQ-508(V) Magnetic Anomaly Detector in a tail stinger can detect the magnetic properties of a submarine’s hull when flying at low-altitude above one.
Air-dropped sonar buoys, however, are one of the primary methods for detecting submerged submarines, and the P-1 can carry thirty-seven in a launcher, plus up to seventy more stowed in the cabin. The diverse sources of sensor data are then fused in an HYQ-3 Battle Command System which also uses an Artificial intelligence to predict the movements of a detected submarines. The HYQ-3 can exchange information with other submarine hunters including the Japanese Navy’s SH-60K helicopters, and link up with a naval database and satellite recon database to identify unknown vessels. The P-1 also has a Link-16 type datalink allowing to share sensor data with platforms such as F-15J jet fighters and 767-AWACS radar planes and Aegis-equipped missile destroyers.
If a P-1’s activities attract unfriendly anti-aircraft missiles, as seems likely in a high-intensity conflict, the P-1 also has an HLQ-9 Missile Warning System, electronic countermeasures and a chaff and flare dispensers to detect and decoy attacks.
In return, the patrol plane can carry up to twenty thousand pounds of weapons on sixteen hardpoints, including eight in an internal bomb bay behind the cockpit and the rest underwing. In addition to depth charges and mines, these include Mark 46 or domestic Japanese lightweight anti-submarine torpedoes, Harpoon or Type 91 ASM-1C sea-skimming subsonic anti-ship cruise missiles, and even AGM-65 Maverick precision-guided missiles.
By mid-2018, fifteen P-1 were in service with the Japanese’s Naval Self-Defense Force’s Air Patrol Squadron 3 based at Atsugi, and the VX-51 testing unit, with twenty more on order. While operational details are sparse, an official told Aviation Week that P-1s were “routinely detecting submarines at longer ranges than was possible with the P-3 from both medium and low altitudes.”
Tokyo eventually intends on operating sixty to seventy P-1s to replace all its P-3Cs, and plans on routinely upgrading the P-1’s sensors every ten years. The JSDF may also procure customized P-1s to replace P-3 variants, which include five EP-3C signals intelligence planes, four OP-3C optical reconnaissance aircraft, and four UP-3C and UP-3D test and training planes.
In 2014, Japan relaxed its rule on exporting military hardware, and began marketing the P-1 abroad—but so far the Poseidon has edged it out with contracts with New Zealand the United Kingdom. The Kawasaki design costs between $140 and 160 million each, while the Poseidon apparently has a fly-away cost of $125-150 million, though its original procurement cost was $250 million. Nonetheless, Thailand and Vietnam have expressed interest, and Japan has proposed the P-1 to France and Germany as a replacement for aging Atlantic 2 patrol planes. However, advantages in the U.S. military procurement network and the availability of 737 parts may tilt the odds against the P-1.
Still, the P-1 seems to to have several small edges over the P-8 due to its superior low-altitude flight performance, higher maximum speed while transiting, additional weapons hardpoints (sixteen rather than eleven), flexibility from it four engines, and the incorporation of a MAD sensor. (Most Poseidons, save the P-8Is operated by the Indian Navy, lack them.) To be fair, directly comparing the aircrafts’ respective sensor suites is difficult without hands-on experience. A rare opportunity to do so came this June 2018 during the Mallabar anti-submarine exercise, in which a Japanese P-1 participated alongside U.S. and Indian Navy P-8s.
Whether or not the premium airborne submarine hunter finds customers abroad, Tokyo ultimately hopes platforms like the P-1 and its Soryu-class Air Independent Propulsion submarines will protect it from China’s growing submarine fleet.