Slicing silently through the depths of the South China Sea, a Japanese submarine is on patrol in the shipping lanes near the Raiu Islands. It’s early morning and the crew has been at sea for 8 days, underwater for nearly 48 hours. They will soon need to surface to recharge their electric batteries. On the surface, the submarine will run its air-breathing generators and recharge the batteries so they can get back safely below the waterline. During WWII, diesel and electric submarines spent the majority of their time on the surface where they could travel much quicker, even on patrol. The problem with being on the surface is that it makes the boat vulnerable to attack.

At the command of the boat captain, the crew quickly gets to work bringing the submarine up to periscope depth. The captain follows the periscope upward and begins to spin the viewer around in a 360-degree sweep of the area to ensure there aren’t any warships or aircraft waiting on top. It appears that the area is clear and he gives the command to surface. What the captain missed was an American PBY-5 Catalina patrol plane that was passing to the rear of the submarine. The copilot spotted the wake where the periscope was slicing through the water. The aircraft makes its turn toward the underwater vessel and soon the submarine crew will realize their error.

The patrol aircraft was fortunate enough to be at a low altitude and at the right place and time to spot the periscope. As it lines up with the submarine, the pilots realize the submerged boat is surfacing. On this first pass, while the submarine is unaware of the plane’s existence, the pilot needs to be perfect when he drops the depth charges.

Air Anti-Submarine Warfare (ASW)

In WWII, aircraft relied on detecting submarines through the use of lookouts. The planes were limited to attacking by strafing the submarines with guns, dropping depth charges, and firing rockets.

During the Cold War, aircraft radar systems were developed to effectively locate submarines when their periscopes came above the waterline. Over the decades as radars become more powerful they could eliminate more clutter (unwanted echoes) on the water surface that would make it difficult to locate a periscope. Radars have also become more powerful so they allow an aircraft to operate at higher altitudes.

A submarine’s best defense is being hidden well below the surface so that it cannot be detected. If you want to keep your submarine hidden then it is likely that you want to keep the periscope below the surface too. As small as a periscope may seem on the open ocean, they are detectable by the most sophisticated radar systems like what is found in the U.S. Navy’s P-3 Orion and its replacement, the P-8 Poseidon. The P-3 Orion has been the U.S. Navy’s maritime surveillance aircraft since its introduction in August of 1962. The P-8 Poseidon has been in service since 2013 and will be the replacement for the aging P-3 over the coming years. Currently, the U.S. Navy has forty-one P-3 Orions in service (as of 2019). The Navy also has ninety-one P-8 Poseidon aircraft and another twenty-four on order. Both aircraft are flown by other countries also, but due to cost and availability, the older P-3 is much more prolific.

P-3 Orion

USN P-3C showing the MAD (rear boom)

Underside view of a USN P-3C showing the MAD (rear boom) and external sonobuoy launch tubes (grid of black spots towards the rear)

The P-3 Orion, which is based on the L-88 Electra Airliner, has four turboprop engines and is used for both anti-submarine and maritime surveillance. It is a land-based, long-range patrol aircraft designed to be a Cold War eye-in-the-sky to track Soviet submarines. The distinctive long metal boom that extends off the back of the aircraft is for the magnetic detection of submarines. The boom is situated at the rear of the aircraft to avoid interference with the plane’s electronics and metal frame. Even with powerful radar systems, the P-3 still uses crew members for observation. For an extended patrol, when the P-3 arrives on station the pilots will cut off the two outer engines, one port, and one starboard, to conserve fuel. This not only saves fuel but also reduces engine exhaust, improving the visibility of a crew member manning the aft observer station.

The United States Navy’s P-3 has a full complement of avionics that allows its crew to monitor highly sophisticated electronic detection gear like sonobuoys and radar systems. When it comes to attacking an enemy submarine or surface vessel, the P-3 can carry torpedoes, depth charges, bombs, and rockets, including the AGM-84 Harpoon anti-ship missile.

The Orion carries a crew of eleven. It has a maximum speed of 466 mph and a cruising speed of 379 with a ceiling of 28,300 feet. For low-altitude surveillance, the P-3 can cruise slowly above striking distance of ground fired rockets. This allows for land surveillance over hostile territory, as it was used during Operation Desert Storm, to monitor Iraqi troop movements and assess battle damage. It has the ability to fly 16-hour missions and has a ferrying range of over 5500 miles.

P-8 Poseidon

A P-8A of VP-16 dropping a Mark 46 torpedo

A P-8A of VP-16 dropping a Mark 46 torpedo

With its introduction into service with the United States Navy in November of 2013, this twin turbofan submarine hunter strikes fear in any enemy fleet. The P-8 is based on Boeing’s 737-800 aircraft and is outfitted with the best avionics and radar equipment available anywhere. Unlike the commercial 737 models, the P-8 has a stronger airframe and 50% thicker skin to harden its body so it can withstand the strain of low flight over the ocean. Every surface of the P-8 has the capability of deicing.

This powerful, high-tech maritime patrol plane flies at a speed of 563 mph, over 200 mph faster than the P-3 it is due to replace. It also has a range of nearly 4500 miles without refueling. This means it can deploy and get onto a patrol station much more quickly than its predecessor. If needed, it can then redeploy to another patrol area much faster than a P-3.

The Poseidon is a sophisticated tracker that has a ceiling of 41,000 feet and does most of its work at this high altitude. The importance of locating a ship or submarine amongst the high clutter area of the ocean has been discussed above. The P-8 Poseidon has a very powerful APY-10 multifunction radar. It’s a mechanically scanned radar system that’s optimized for maritime, littoral, and overland surveillance. It can locate and track not only surface ships but easily locates those submarine periscopes from very high altitudes. Compared to the P-3’s APS-137 radar, the APY-10 is smaller, lighter, and uses less power. With its wide range of powerful image intensifiers, sensors, and infrared turret, the P-8 can provide clear and sharp imagery of ports, cities and surveil along coastlines or inland from a long-range standoff patrol area. The infrared sensor can detect the heat from submarines or even fires. The Poseidon can also deploy new sonar buoys that last longer and have a broader search range.

Also read Duotech’s article: APS-137 Radar Enables the P-3 Orion to Fight Pirates

The Poseidon also possesses an electronics support measures (ESM) system designated the ALQ-240. Through the use of precise direction finding and geo-location capabilities, this system allows the P-8 crew to search, intercept, identify, and locate an enemy radar or their radio communications. It can do this while passively monitoring a large area without being detected.

The Poseidon has a crew of nine; two flight crew and seven mission crew members. This flight crew is not only able to stealthily find ships and submarines but is also quite lethal when necessary to eliminate a threat. The P-8 has five internal bays and six external hardpoints to carry air-launched cruise missiles, anti-ship missiles, torpedos, mines, and depth charges.

A Growing Need for Maritime Surveillance

Not since the Cold War has submarine detection taken on such a prominent mission for NATO. With both Russia and China strengthening their own Navies, adding more submarines and improving their capabilities, the use of maritime patrol aircraft to keep up with their locations has become vital. With the increase in tensions between NATO countries and Russia, the activity of submarines has greatly increased around the world. Though the Russian fleet is not as large as it was during the Cold War, their submarines are highly sophisticated and have been deployed to all regions around the world. The P-8 Poseidon is one of the best maritime intelligence and surveillance aircraft and is the current best solution to locate, track, and monitor submarines anywhere. It is a popular platform for other countries seeking the best solution for Multimission Maritime Aircraft. Australia will purchase up to 15 P-8 aircraft, nine for the United Kingdom, New Zealand four, and other countries like Canada, South Korea, and Turkey are strongly considering it.

Since 1962, over 700 P-3s have been manufactured and commissioned worldwide. The P-3 Orion is still in service with many countries including the United States. Until the last P-3 is decommissioned, it will remain a critical tool in the US Navy’s mission as well as the numerous other operators it serves.

The radar system of any aircraft is very important to ensure the safety of the crew and the success of the mission. The P-3 Orion’s APS-137 radar system not only performs to protect a flight crew’s safety, but also enables the United States Navy to locate and track submarines and surface ships, support and carry out U.S. military operations, and provide protection of international trade relationships with allies.

r-2605 aps-137 radar systemPictured here is the receiver-pulse compressor R-2308A of the AN/APS-137. Duotech has extensive test and repair capabilities for the antenna assembly, receiver/transmitter, radar processor, and the indicator of the APS-137. Other important systems of the P-3 must be maintained to avoid scrapping due to obsolescence like the subsystems of the ASA-64 Magnetic Compensator Group.

Repairing Obsolete Equipment

To keep aging platforms like the P-3 Orions flying these systems must still be maintained even when facing obsolescence issues. Avoiding scrapping repairable parts requires a depot to develop the missing technical data or reverse engineer broken or missing parts. Duotech specializes in repairing obsolete equipment that the OEMs no longer support, or if they do, the repair comes at a cost well over repair percentage guidelines.

For companies who only need one or a few items repaired, we are responsive to their small quantity repair requirements. For equipment that does not have documentation or has unavailable parts, Duotech is able to reverse engineer and develop technical data. Instead of scrapping repairable equipment, we offer solutions to keep your legacy aircraft in the air and your obsolete mission-critical equipment functioning.

DSI is a qualified FAA Repair Station and maintains AS9100D and ISO 9001 certifications with the scope of repair, design, production (including CNC machining and laser cutting), testing and overhaul services for electronic and electro-mechanical equipment for military and commercial applications. Duotech has the capability to repair the mission-critical electronics systems of the E-3 Sentry, P-3 Orion, and C-130 Hercules aircraft.

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