It’s low light, and the blue sky melts into brilliant oranges and pinks as the sun sets low on the ocean’s horizon. The silhouette of a very large cargo ship sails quietly across the sea, fourteen miles out of the Port of Charleston (SC) on its way to destinations unknown. On its bridge, the ship’s lookout scans the waters surrounding the ship, looking for any other ships or objects that would present a hazard to the cargo ship. Slowly, he guides his binoculars across the seas and something catches his eye. He focuses his eyes more on where he thinks he saw a slender black tube protruding from the water. He can’t believe what he sees as he locates a periscope just before it disappears under the surface. He tells the officer of the watch what he is confident he just saw. The captain of the ship notes the boat’s current location and transmits to shore what was observed.

Communications quickly get to U.S. Navy, who immediately launches a P-8A Poseidon from its home base at Naval Air Station Jacksonville. With a top speed of 564 mph, the P-8 is able to get on station quickly and begin the hunt for the possible submarine.

Both the U.S. Coast Guard and U.S. Navy dispatch ships and helicopters to the area at top speed to the area. In a team effort, all of these resources scour the area using coordinated search patterns. Ships launch sonobuoy detection devices over their bows and helicopters dip low-frequency sonar listening devices into the dark water below. From 30,000 feet, the P-8 scans the ocean using its very powerful APS-149 radar that can detect periscopes at extremely long distances.

After 8 hours of searching for the possible submarine, it is never located and the hunt is called off. Whether there was an unknown submarine that close to the American coastline goes unanswered, but this investigation did provide a real life training opportunity between air, surface, and subsurface anti-submarine warfare (ASW) assets together.

Submarine Warfare

Around 1620, the world’s first working prototype submarine was built by Cornelius Drebbel for British King James I. Likely an upside-down rowboat that was sealed to maintain the air under it, Drebbel demonstrated it in the River Thames in front of the king and thousands of other onlookers.

It would be in September 1775, during the American Revolutionary War that the first submarine would be used for the first time to attack a ship. The Turtle, as it would be called, was a wooden underwater craft that allowed one man to control different cranks and levers to maneuver just below the water’s surface. The operator could approach a ship and screw 150 pounds of gunpowder to the hull. The Turtle was unsuccessful on its first use attacking the British warship HMS Eagle. It would be lost when the ship carrying it was sunk shortly after.

Submarines in the Beginning

Between the Revolutionary War and Civil War, submarines continued to develop with new innovations to make them more successful, like storing compressed air on board, adding conning towers, and using ballast tanks for help with buoyancy. During the Civil War, the Confederacy utilized a submarine called the H.L. Hunley to attack and sink a Union ship in the Charleston, SC harbor. The Hunley drove its torpedo in the USS Housatonic. The explosion sunk the ship but also the Hunley, killing all the men inside.

Submarines During the World Wars

During World War 1 and 2, submarines began to play a much more significant role in combat as the Allies and Axis members fought to control the Pacific and Atlantic Oceans. Germany employed their U-boats so effectively against allied shipping in WWII that Britain and the United States quickly modernized their own submarines. The United States would not only become very effective at attacking military and merchant vessels but also would utilize the subs to secretly insert special operations teams into hostile areas and rescue downed American pilots.

Cold War Submarines

Since the Cold War began and to this day, advancements in submarine technologies have made them even more silent and deadly. With nuclear power, submarines greatly improved the ability to hide from sight for periods of up to three months without surfacing. These improvements made them even more concerning. A submarine captain can station his underwater vessel off a nation’s shoreline and secretly listen to communications, gather information, monitor shipping routes, and determine warship locations.

Anti-Submarine Warfare

Submarines can pose a great danger to a nation’s security. Since a submarine can move about undetected, hidden under the sea, knowing an enemy sub’s location as often as possible is very important. The practice of hunting, locating, tracking, damaging, and destroying submarines is called Anti-Submarine Warfare (ASW).

Prior to WW1, submarine warfare was not a priority and therefore anti-submarine warfare tactics were primitive. Some earlier defensive tactics involved battleships skirting their hulls with chainlink nets to protect from torpedos. Nets were also used to span the mouth of a harbor to keep submarines out. Grappling hooks drug behind ships and attacking the periscopes with hammers were other attempts at foiling submarine attacks.

World War I

Early on in WW1, anti-submarine warfare still consisted of attacking a submarine as you would a ship. Submarines would have to come to the surface for navigation, resupply, and to confirm targets. Surface ships would attack them at this vulnerable time with explosives or even by ramming them. German submarines, known as u-boats, would not surface if they faced a warship and therefore exposing themselves to attack. Because of this, the British used Q-ships, heavily armed boats disguised as unarmed merchant ships to trick the u-boats into surfacing. The Q-ships disguised (hid) their weapons from view and then attacked as soon as the u-boats surfaced.

Germany’s u-boats proved their effectiveness at controlling shipping lanes around Britain by attacking and sinking cargo ships, warships, and even passenger ships. In response to the attacks on merchant ships and passenger liners, military escort ships were added to convoys of merchant ships to provide security. This was a time when the first sonar technology was developed and seaplanes were introduced to hunt the u-boats. This same era introduced depth charges as a new way to destroy the underwater killers after they disappeared underwater.

Following WW1

Between the World Wars, sonar was further developed, as were range recorders. The range detectors helped determine the distance from a ship to a submarine by listening to the underwater sounds the u-boat propellers made. These technologies were added to military ships dedicated to hunting submarines.

World War II

In World War II, the initial way to defend against submarines was to use sonar to locate them and attack using depth charges. The use of submarines by both Axis and Allies became a major offensive tool for the countries that possessed them. Especially affected would be countries that depended on imports of food and other supplies like the island nations of Britain and Japan.

Some of the improvements to anti-submarine warfare in WWII would include speeding convoys up in order to make them more difficult to target, as well as greatly increasing the number of small warships used for convoy security. Hunter Killer groups of ships and planes were established to actively hunt for submarines instead of waiting for the submarines to attack a convoy. Sub-hunting aircraft were outfitted with better radar and much improved air-drop homing torpedoes. With these additions, they became the most effective way to hunt and kill submarines.

Cold War ASW

World War II demonstrated the importance of submarines in control of the seas. As the world’s superpowers moved into the Cold War era, they strengthened their navies. This meant always improving their submarine capabilities. In the first fifteen years following WWII, the submarine went from a weapon that could only stay submerged for short periods of time to becoming much faster, quieter, and long-lasting beneath the surface. These improvements, along with more sophisticated electronic sensors and weapons, allowed the submarines to better operate at sea alone.

When submarines began using nuclear power, it changed everything. The first launch was the USS Nautilus in 1954. Now they could submerge indefinitely, parked silently off the coast with a nuclear payload, remaining hidden for even more extended periods of time. With these threats, locating and deterring submarines has become an even more important goal.

When it came to attacking submarines, torpedoes replaced depth charges. Torpedoes that used acoustics to locate their target would become very effective at locating submarines underwater. Torpedoes became more sophisticated in technology using wire and optical guidance to locate their targets, which greatly improved their lethality.

Anti-Submarine Warfare Today

Since the early days of the Cold War, underwater passive sonar sensors, like Sound Surveillance System (SOSUS), have tracked subs from the seafloor at major chokepoints across the globe like the Greenland-Iceland-United Kingdom (GIUK) gap.

As submarines became much faster, quieter, and more lethal, hunter-killer groups, an interconnected network of ships, aircraft, and other submarines, needed even better sensing technology to locate and track the enemy submarines. Long-range patrol aircraft like the U.S. Navy’s P-3 Orion and P-8 Poseidon make up hunter-killer groups, along with surface ships, to find submarines.

P-3 Orion Anti-submarine and Maritime Surveillance Aircraft

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.

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

P-8 Poseidon Anti-submarine and Maritime Surveillance Aircraft

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 Poseidon 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’ is a mechanically scanned radar system that’s optimized for maritime, littoral, and overland surveillance. It can locate and track not only surface ships but can easily locate 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 and cities, and can 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.

The Future of ASW

The future of Anti-Submarine Warfare could lie in unmanned surface ships, like the ASW Continuous Trail Unmanned Vessel (ACTUV) Sea Hunter. This unmanned surface vessel will track enemy diesel-electric submarines in shallow water as well as gather intelligence and provide surveillance and launch/recover underwater unmanned vehicles (UUV) without a person on board. It will likely become the future of sea patrol.
Video: Sea Hunter – World’s Largest Unmanned Drone

Another future of ASW lies in UUV or unmanned underwater vehicles. These small, lightweight, low-cost weapons can be fired from warships or even a commercial surface vessel masquerading as a fishing trawler. Once launched, the networked UUVs work together like a swarm of bees to attack a target.

Though its not expected to happen soon, unmanned technologies like the Sea Hunter and UUVs could provide enough of a threat to a submarine’s stealth that they could become a thing of the past.

The future of anti-submarine warfare


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