How Submarines Work

Submarines are incredible pieces of technology. Not so long ago, a naval force worked entirely above the water; with the addition of the s­ubmarine to the standard naval arsenal, the world below the surface became a battleground as well.

Submarine Image Gallery

MYCHELE DANIAU/AFP/Getty Images
The French submarine Le Terrible is inaugurated on March 21, 2008, in Cherbourg, France. Le Terrible was developed entirely through computer-assisted design and will begin service in 2010. See more submarine pictures.

The adaptations and inventions that allow sailors to not only fight a battle, but also live for months or even years underwater are some of the most brilliant developments in military history.

In this , we will see how a submarine dives and surfaces in the water, how life support is maintained, how the submarine gets its power, how a submarine finds its way in the deep ocean and how submarines might be rescued.

Diving and Surfacing

Photo courtesy U.S. Navy

­ A submarine or a ship can float because the weight of water that it displaces is equal to the­ weight of the ship. This displacement of water creates an upward force called the buoyant force and acts opposite to gravity, which would pull the ship down. Unlike a ship, a submarine can control its buoyancy, thus allowing it to sink and surface at will.

To control its buoyancy, the submarine has ballast tanks and auxiliary, or trim tanks, that can be alternately filled with water or air (see animation below). When the submarine is on the surface, the ballast tanks are filled with air and the submarine's overall density is less than that of the surrounding water. As the submarine dives, the ballast tanks are flooded with water and the air in the ballast tanks is vented from the submarine until its overall density is greater than the surrounding water and the submarine begins to sink (negative buoyancy). A supply of compressed air is maintained aboard the submarine in air flasks for life support and for use with the ballast tanks. In addition, the submarine has movable sets of short "wings" called hydroplanes on the stern (back) that help to control the angle of the dive. The hydroplanes are angled so that water moves over the stern, which forces the stern upward; therefore, the submarine is angled downward.

Buoyancy in a submarine. Click on the Surface and Submerge
buttons to watch buoyancy in action.

To keep the submarine level at any set depth, the submarine maintains a balance of air and water in the trim tanks so that its overall density is equal to the surrounding water (neutral buoyancy). When the submarine reaches its cruising depth, the hydroplanes are leveled so that the submarine travels level through the water. Water is also forced between the bow and stern trim tanks to keep the sub level. The submarine can steer in the water by using the tail rudder to turn starboard (right) or port (left) and the hydroplanes to control the fore-aft angle of the submarine. In addition, some submarines are equipped with a retractable secondary propulsion motor that can swivel 360 degrees.

When the submarine surfaces, compressed air flows from the air flasks into the ballast tanks and the water is forced out of the submarine until its overall density is less than the surrounding water (positive buoyancy) and the submarine rises. The hydroplanes are angled so that water moves up over the stern, which forces the stern downward; therefore, the submarine is angled upward. In an emergency, the ballast tanks can be filled quickly with high-pressure air to take the submarine to the surface very rapidly.

Life Support

There are three main problems of life support in the closed environment of submarine:

• Maintaining the air quality
• Maintaining a fresh water supply
• Maintaining temperature

Maintaining the Air Quality
The air we breathe is made up of significant quantities of four gases:

• Nitrogen (78 percent)
• Oxygen (21 percent)
• Argon (0.94 percent)
• Carbon dioxide (0.04 percent)

When we breathe in air, our bodies consume its oxygen and convert it to carbon dioxide. Exhaled air contains about 4.5 percent carbon dioxide. Our bodies do not do anything with nitrogen or argon. A submarine is a sealed container that contains people and a limited supply of air. There are three things that must happen in order to keep air in a submarine breathable:

• Oxygen has to be replenished as it is consumed. If the percentage of oxygen in the air falls too low, a person suffocates.
• Carbon dioxide must be removed from the air. As the concentration of carbon dioxide rises, it becomes a toxin.
• The moisture that we exhale in our breath must be removed.

Oxygen is supplied either from pressurized tanks, an oxygen generator (which can form oxygen from the electrolysis of water) or some sort of "oxygen canister" that releases oxygen by a very hot chemical reaction. (You may remember these canisters because of their problems on the MIR space station -- see this page for details). Oxygen is either released continuously by a computerized system that senses the percentage of oxygen in the air, or it is released in batches periodically through the day.

Carbon dioxide can be removed from the air chemically using soda lime (sodium hydroxide and calcium hydroxide) in devices called scrubbers. The carbon dioxide is trapped in the soda lime by a chemical reaction and removed from the air. Other similar reactions can accomplish the same goal.

The moisture can be removed by a dehumidifier or by chemicals. This prevents it from condensing on the walls and equipment inside the ship.

In addition, other gases such as carbon monoxide or hydrogen, which are generated by equipment and cigarette smoke, can be removed by burners. Finally, filters are used to remove particulates, dirt and dust from the air.

Maintaining a Fresh Water Supply
Most submarines have a distillation apparatus that can take in seawater and produce fresh water. The distillation plant heats the seawater to water vapor, which removes the salts, and then cools the water vapor into a collecting tank of fresh water. The distillation plant on some submarines can produce 10,000 to 40,000 gallons (38,000 - 150,000 liters) of fresh water per day. This water is used mainly for cooling electronic equipment (such as computers and navigation equipment) and for supporting the crew (for example, drinking, cooking and personal hygiene).

Maintaining Temperature
The temperature of the ocean surrounding the submarine is typically 39 degrees Fahrenheit (4 degrees Celsius). The metal of the submarine conducts internal heat to the surrounding water. So, submarines must be electrically heated to maintain a comfortable temperature for the crew. The electrical power for the heaters comes from the nuclear reactor, diesel engine, or batteries (emergency).

Power Supply

­ Nuclear submarines use nuclear reactors, steam turbines and reduction ge­aring to drive the main propeller shaft, which provides the forward and reverse thrust in the water (an electric motor drives the same shaft when docking or in an emergency).

Submarines also need electric power to operate the equipment on board. To supply this power, submarines are equipped with diesel engines that burn fuel and/or nuclear reactors that use nuclear fission. Submarines also have batteries to supply electrical power. Electrical equipment is often run off the batteries and power from the diesel engine or nuclear reactor is used to charge the batteries. In cases of emergency, the batteries may be the only source of electrical power to run the submarine.

A diesel submarine is a very good example of a hybrid vehicle. Most diesel subs have two or more diesel engines. The diesel engines can run propellers or they can run generators that recharge a very large battery bank. Or they can work in combination, one engine driving a propeller and the other driving a generator. The sub must surface (or cruise just below the surface using a snorkel) to run the diesel engines. Once the batteries are fully charged, the sub can head underwater. The batteries power electric motors driving the propellers. Battery operation is the only way a diesel sub can actually submerge. The limits of battery technology severely constrain the amount of time a diesel sub can stay underwater.

Because of these limitations of batteries, it was recognized that nuclear power in a submarine provided a huge benefit. Nuclear generators need no oxygen, so a nuclear sub can stay underwater for weeks at a time. Also, because nuclear fuel lasts much longer than diesel fuel (years), a nuclear submarine does not have to come to the surface or to a port to refuel and can stay at sea longer.

Nuclear subs and aircraft carriers are powered by nuclear reactors that are nearly identical to the reactors used in commercial power plants. The reactor produces heat to generate steam to drive a steam turbine. The turbine in a ship directly drives the propellers, as well as electrical generators. The two major differences between commercial reactors and reactors in nuclear ships are:

• The reactor in a nuclear ship is smaller.

• The reactor in a nuclear ship uses highly enriched fuel to allow it to deliver a large amount of energy from a smaller reactor.

Navigation

­ Light does not penetrate very far into the ocean, so submarines must nav­igate through the water virtually blind. However, submarines are equipped with navigational charts and sophisticated navigational equipment. When on the surface, a sophisticated global positioning system (GPS) accurately determines latitude and longitude, but this system cannot work when the submarine is submerged. Underwater, the submarine uses inertial guidance systems (electric, mechanical) that keep track of the ship's motion from a fixed starting point by using gyroscopes. The inertial guidance systems are accurate to 150 hours of operation and must be realigned by other surface-dependent navigational systems (GPS, radio, radar, satellite). With these systems onboard, a submarine can be accurately navigated and be within a hundred feet of its intended course.

Photo courtesy U.S. Department of Defense Sonar station onboard the USS La Jolla nuclear-powered attack submarine

To locate a target, a submarine uses active and passive SONAR (sound navigation and ranging). Active sonar emits pulses of sound waves that travel through the water, reflect off the target and return to the ship. By knowing the speed of sound in water and the time for the sound wave to travel to the target and back, the computers can quickly calculate distance between the submarine and the target. Whales, dolphins and bats use the same technique for locating prey (echolocation). Passive sonar involves listening to sounds generated by the target. Sonar systems can also be used to realign inertial navigation systems by identifying known ocean floor features .

Rescue

­­ W­hen a submarine goes down because of a collision with something (such as another vessel, canyon wall or mine) or an onboard explosion, the crew will radio a distress call or launch a buoy that will transmit a distress call and the submarine's location. Depending upon the circumstances of the disaster, the nuclear reactors will shut down and the submarine may be on battery power alone.

If this is the case, then the crew of the submarine have four primary dangers facing them: ­

• Flooding of the submarine must be contained and minimized.
• Oxygen use must be minimized so that the available oxygen supply can hold out long enough for possible rescue attempts.
• Carbon dioxide levels will rise and could produce dangerous, toxic effects.
• If the batteries run out, then the heating systems will fail and the temperature of the submarine will fall.

­ Rescue attempts from the surface must occur quickly, usually within 48 hours of the accident. Attempts will typically involve trying to get some type of rescue vehicle down to remove the crew, or to attach some type of device to raise the submarine from the sea floor. Rescue vehicles include mini-submarines called Deep-Submergence Rescue Vehicles (DSRV) and diving bells.

Photo courtesy U.S. Department of Defense DSRV secured to the deck of a submarine

The DSRV can travel independently to the downed submarine, latch onto the submarine over a hatch (escape trunk), create an airtight seal so that the hatch can be opened, and load up to 24 crew members. A diving bell is typically lowered from a support ship down to the submarine, where a similar operation occurs.

To raise the submarine, typically after the crew has been extracted, pontoons may be placed around the submarine and inflated to float it to the surface. Important factors in the success of a rescue operation include the depth of the downed submarine, the terrain of the sea floor, the currents in the vicinity of the downed submarine, the angle of the submarine, and the sea and weather conditions at the surface.

Different Types Of Submarines

This Project 877EKM submarine, type Varshavyanka (Kilo Class according to the NATO designation), was built in 1988 for the Indian Navy by the Leningrad Admiralty Shipyard Association according to the project developed by the Rubin Central Design Bureau for Marine Engineering. The Navy of this friendly country has several submarines of that kind and, in terms of their combat and sea-going capabilities, they are well received by Indian submariners. Following its intensive operation, the need arose to repair INS Sindhuvir's sophisticated mechanisms and equipment. The Indian Navy (IN) Command took a decision to repair the submarine in Russia.

INS Sindhuvir sailing in the high seas

Among several Russian ship repair facilities, the choice fell on the Severodvinsk-based Zvyozdochka State Mechanical Engineering Enterprise, a specialized ship repair facility. The enterprise dates back to 1956 when it began to repair fishing vessels, tugs and transport ships. At present, Zvyozdochka is a recognized domestic ship repair leader. The enterprise has mastered the repair of diesel-electric submarines and optimized the technology of repair and modernization of nuclear-powered submarines. Commissioning of its first nuclear-powered submarine was a landmark in the history of the enterprise: the submarine's nuclear power plant was repaired and a new underwater-launched missile system installed. With the commissioning of a specialized production shop in 1974, the enterprise became the largest producer of propellers made of high-strength stainless steels, carbon steels, non-ferrous and titanium alloys, including those designed for nuclear-powered submarines, icebreakers, and cruise superliners. Every year the enterprise manufactures over 1000 propellers weighing from 20 kilograms to 50 tons.

The prestige of Zvyozdochka increased with the introduction of the Onega Research & Development Technological Bureau - elaborated technology involving the industrial method of re-equipment, modernization and repair of submarines of Projects 627A, 658M, 667A, 667B, 667BD, 667BDR and 667BDRM. Owing to this method, up to four submarines went down the slipways of the enterprise every year. And, most importantly, the submarines left the launching dock after repair with improved acoustic characteristics. Having repaired and modernized over 100 first, second and third-generation submarines, Zvyozdochka is currently able to repair ships of any class and purpose and even build new-project ships and vessels.

Today, Zvyozdochka is a comprehensive and well-equipped facility boasting hi-tech production potential. The enterprise has two covered berths with slipways, a floating dock, quays equipped with portal cranes, as well as main shops (hull building, pipe and copper works, outfitting shops, etc.), repair and assembly, machine-building and auxiliary shops. Zvyozdochka is fully engaged in ship repair and shipbuilding activities, including assembly, hull repair, docking, paintwork, electroplating, mechanical and propeller machining work, as well as repair of ship mechanisms and equipment. Main two-span covered berth No.1 features a total length of 216 metres, while the slipway is 204 metres long. Each span is equipped with a bridge crane with a load-lifting capacity of 100 tons. The slipway facility incorporates a flooding dock with portal cranes with a load-lifting capacity of 30 and 80 tons respectively, a transborder pit, self-propelled transborders for transverse movement of vessels, and self-propelled transport facilities for longitudinal movement of vessels.

Each facility features a load-lifting capacity of 12,500 tons. The floating dock is provided with a 139.5 m floor. The special and deep-water quays are equipped with two-three portal cranes with a load-lifting capacity of up to 80 tons. Each quay is provided with a plant to supply high-pressure nitrogen and air, low-pressure air and foam, fresh cold and hot water, electric power with required characteristics, and high-pressure steam. The hull-building shop with a working area of 9700 m² has hi-tech equipment, a steel cleaning line, automated gas, plasma and oxygen-cutting machines, sheet bending power presses and rolls, and machine tools for machining edges of large-sized parts for welding. The pipe and copper works shop ensures all operations involving the bending and machining of pipes and tubes of 57 to 273 mm in diameter by means of unique equipment, as well as insulation and coating of comprehensive configuration pipes and tubes. The modern submarine cannot be visualized without anti-sonar coating that is prepared and applied by the special coating and painting shop.

INS Sindhuvir after repair

One of the main shops in ship repair technology is the outfitting shop furnished with heavy-duty press-forging and highly productive welding equipment. This shop also repairs and manufactures shipboard equipment, ventilation systems, etc. The machine-building, repair/assembly and auxiliary shops enable the Zvyozdochka staff to perform top-quality comprehensive repairs of any-project submarines independently, without involving other enterprises. The modern ship repair level, hi-tech stand and equipment base, highly qualified specialists and a suitable cost of labor attract potential customers' attention. Thus, as Director of the enterprise Nikolai Kalistratov says, India had good reason to choose Zvyozdochka.

In December 1996, the Russian Rosvoorouzhenie State Corporation and India signed a set of contracts for the repair of the Indian Navy's INS Sindhuvir submarine. The contract volume involved the repair of the submarine hull, a number of systems, special technology and equipment as well as modernization. Prior to signing this contract, Zvyozdochka specialists executed large-volume preparatory work at the submarine's home base. They checked the technical condition of the submarine's hull, equipment, and all its systems and compiled a repair sheet incorporating all revealed defects and their remedy.

The contract stipulated rendering services to the submarine's crew: provision of comfortable apartments for officers and their families and hotels for seamen; provision of fully equipped working spaces, all types of communications, motor transport; and also offering an entertainment and recreation program for the submarine's crew. In June 1997, the Dockwise Company (Belgium) delivered the INS Sindhuvir to the Zvyozdochka facility where it was placed on the slipways of shop No.10 which had previously repaired dozens of different types of nuclear-powered submarines.

INS Sindhuvir was repaired in the Zvyozdochka's spacious berth provided with hull machining, welding and assembly, mechanical repair, pipe bending, outfitting, insulation & painting, and machining bays, as well as chemical cleaning, electroplating, and instrumentation and automatic equipment repair shops. All the sub's parts & elements, instruments & devices, systems & equipment were checked, repaired (if required), tested and examined. The results were entered into a computer system to create a repair electronic database. Replacement of a pressure hull section should be specially pointed out from the entire range of work executed on the submarine. The filling of Indian-made storage batteries with electrolyte was executed for the first time in Russia (this work was considerably more complicated than that done on Russian submarines).

Taking a closer look at the submarine repair process, Commodore P. Sakhi, Indian Navy's Attache in Russia, frequently visited the enterprise and met with Director Nikolai Kalistratov, submarine repair department chief Igor Orlov, and other specialists of the enterprise. Owing to a well-organized production process, the enterprise specialists and the Indian submariners worked concertedly and jointly solved all complex problems. As a result, Zvyozdochka repaired the submarine in compliance with the terms of the contract. The day of INS Sindhuvir's departure from the covered berth of Shop No.10, became a holiday not only for the submarine's crew and the enterprise's specialists but also for Severodvinsk inhabitants. The enterprise's central gates were thrown open to local people.

A grand meeting took place before a vast concourse, while a traditional bottle of champagne was broken against the ship's side and the submarine, mounted on the transborder, moved into the launching dock where it was put on water. Further factory tests and running trials of the submarine confirmed the high quality of repair. The Indian submariners were pleased. INS Sindhuvir will be in service with the Indian Navy for many years to come. Meanwhile Shop No.10 is expecting new orders. Actually, the enterprise's advanced technologies, it's high production capacity and unique stand base enable Zvyozdochka to repair two submarines at a time.

INS Kursura

The diesel-electric INS Kursura, commissioned in 1969 at the Baltic Sea port city of Riga (at the time part of the Soviet Union, now the capital of Latvia), was the fourth Foxtrot class submarine to be inducted into the Indian Navy. The submarine was decommisioned in 2001 after serving for almost 31 years and later hauled to RK beach in Vizag and opened as a museum in 2002. It is one of the few Russian built Foxtrot class submarines on display to the public and one of a few submarine museums of its kind in the world. Kursura has a length of over 91 meters (20 m longer than a Boeing 747!). Her sheer size can be fully appreciated as she is placed on a pedestal on the beach.

Indian Navy Submarines

Because of India's substantial coastline totalling 7516.5 kms, submarines, as the third arm of the Indian Navy (seventh largest in the world), were perceived as an integral part in safeguarding India's maritime territory. The Indian Navy currently maintains a fleet of 16 submarines in two naval bases located at Vizag (INS Virbahu) and Mumbai (INS Vajrabahu). Vizag and Mumbai are the bases for the Eastern and Western Naval Commands respectively. A third base, INS Kadamba is envisaged to become the biggest navy port (covering an area of almost 45 km2) east of the Suez Canal when fully completed. The navy base, located at Karwar (northern tip of the Arabian Sea coast of Karnataka), will also have berthing facilities for submarines. Ten diesel-electric patrol submarines built by Germany's HDW (Howaldtswerke-Deutsche Werft), now part of Thyssen Krupp Marine Systems, form the backbone of India's submarine fleet. Submarine retrofitting is handled by Hindustan Shipyard at Vizag.

Indian Navy Submarine Fleet:

• Sindhughosh (Type 877EM, Kilo) - 10 nos, delivered between 1986-2000
• Shishumar (Type 209/1500) - 4 nos, delivered between 1984-1994
• Foxtrot - 2 nos, delivered 1973-1974

Future Submarine Inductions

The Indian Navy has ordered six diesel-electric DCNS Scorpène SSK class submarines to be built at the Mazagon Dock located in Mumbai through a technology transfer tieup with DCNS/Navantia. The first submarine is planned to be inducted in 2012 followed by one per year. A nuclear-powered submarine is reportedly under constuction at Mazagon Dock.

INDIAN NAVAL SQUADRONS

It appears that the Indian Navy does not allocate a certain type of vessel to a particular unit. Rather, different vessel types are assigned to units as they are commissioned and the units often switch to very different vessel types from what they might been equipped with originally. For instance, the 22nd Missile Vessel Squadron currently equipped with Tarantul-I Class corvettes may have been the former 22nd Destroyer Squadron and the 31st Patrol Vessel Squadron currently equipped with Petya-II Class frigates may be the former 31st MCM Squadron. Also note that some squadron numbers are not sequential and often repeat themselves, albeit with different vessel types - such as the 21st Missile Vessel Squadron and 21st MCM Squadron. The list below is incomplete, as it does not include the squadron numbers/locations for the Godavari & Brahmaputra Classes of frigates, the Khukri & Kora Classes of corvettes, the Trinkat & Bangaram Classes of fast patrol vessels and other naval ships.

There appears to be a pattern with the submarine squadron numbers. For instance, the 12th Submarine Squadron could have been the former 12th Frigate Squadron or raised as a new unit, sequentially following the 8th, 9th, 10th and 11th Submarine Squadrons. There are some indications that the Indian Navy has now done away with squadron organizations for most combat units, except for submarines, missile boats and minesweepers. Instead, the Indian Navy has opted for combined task groups. Missile boat squadrons are organized into divisions of four or fewer units. For instance, the 25th Missile Vessel Squadron has the 251 Division, 252 Division, 253 Division and so on. Likewise the 22nd Missile Vessel Squadron has the 221 Division, 222 Division and so on. Please note that although the information currently listed on this page has been identified in print, squadron numbers and vessel types could change. Currently active units are listed separately from other units.

WESTERN NAVAL COMMAND, HQ - MUMBAI

10th Submarine Squadron - INS Vajrabahu @ Mumbai
INS Shishumar S44 – Shishumar Class
INS Shankush S45 – Shishumar Class
INS Shalki S46 – Shishumar Class
INS Shankul S46 – Shishumar Class

12th Submarine Squadron - INS Vajrabahu @ Mumbai
INS Sindhuratna S59 - Sindhugosh Class
INS Sindhukesari S60 - Sindhugosh Class
INS Sindhukirti S61 - Sindhugosh Class
INS Sindhuvijay S62 - Sindhugosh Class
INS Sindhurakshak S63 - Sindhugosh Class
INS Sindhushastra S65 - Sindhugosh Class

? Destroyer Squadron @ Mumbai
INS Delhi D61 - Delhi Class
INS Mysore D60 - Delhi Class
INS Mumbai D62 - Delhi Class

? Destroyer Squadron @ Mumbai
INS Ranvir D54 - Rajput Class
INS Ranvijay D55 - Rajput Class

15th Frigate Squadron - INS Agnivahu @ Colaba, Mumbai
INS Talwar F40 - Talwar Class
INS Trishul F41 - Talwar Class
INS Tabar F42 - Talwar Class

22nd Missile Vessel Squadron (K22) - INS Agnivahu @ Colaba, Mumbai
INS Veer K40 - Veer Class
INS Nirbhik K41 - Veer Class
INS Nipat K42 - Veer Class
INS Nishank K43 - Veer Class
INS Nirghat K44 - Veer Class
INS Vibhuti K45 - Veer Class
INS Vipul K46 - Veer Class
INS Vinash K47 - Veer Class
INS Vidyut K48 - Veer Class
INS Nashak K83 - Veer Class
INS Pralaya K91 - Veer Class
INS Prabal K92 - Veer Class

23rd Patrol Vessel Squadron (P23) @ Mumbai
INS Abhay P33 - Abhay Class
INS Ajay P34 - Abhay Class
INS Akshay P35 - Abhay Class
INS Agray P36 - Abhay Class

? Patrol Vessel Squadron @ Mumbai
INS Sukanya P50 - Sukanya Class (Large Patrol Craft)
INS Subhadra P51 - Sukanya Class
INS Suvarna P52 - Sukanya Class

19th MCM Squadron (M19) @ Mumbai - Ocean Minesweepers
INS Pondicherry M61 - Pondicherry Class
INS Porbandar M62 - Pondicherry Class
INS Bedi M63 - Pondicherry Class
INS Bhavnagar M64 - Pondicherry Class
INS Alleppey M65 - Pondicherry Class
INS Ratnagiri M66 - Pondicherry Class

Other Boats @ Mumbai

INS Viraat R22 - Aircraft Carrier

INS Jyoti A58 - Replenishment Tanker

INS Shakti A57 - Replenishment Tanker

INS Nireekshak A15 - Diving Support Ship

INS Investigator J15 - Sandhayak Class (Survey Ship)

EASTERN NAVAL COMMAND, HQ - VIZAG

8th Submarine Squadron - INS Virbahu @ Vizag
INS Vela S40 - Foxtrot Class
INS Vagli S42 - Foxtrot Class

11th Submarine Squadron - INS Virbahu @ Vizag
INS Sindhughosh S55 - Sindhugosh Class
INS Sindhudhvaj S56 - Sindhugosh Class
INS Sindhuraj S57 - Sindhugosh Class
INS Sindhuvir S58 - Sindhugosh Class

? Destroyer Squadron @ Vizag
INS Rajput D51 - Rajput Class
INS Rana D52 - Rajput Class
INS Ranjit D53 - Rajput Class

14th Frigate Squadron @ Vizag
INS Udaygiri F35 - Nilgiri Class
INS Dunagiri F36 - Nilgiri Class
INS Taragiri F41 - Nilgiri Class
INS Vindhyagiri F42 - Nilgiri Class

21st MCM Squadron (M21) @ Vizag - Ocean Minesweepers
INS Karwar M67 - Pondicherry Class
INS Cannanore M68 - Pondicherry Class
INS Cuddalore M69 - Pondicherry Class
INS Kakinanda M70 - Pondicherry Class
INS Kozhikode M71 - Pondicherry Class
INS Konkan M72 - Pondicherry Class

Other Boats @ Vizag

INS Sandhayak J18 - Sandhayak Class (Survey Ship)
INS Nirdeshak J19 - Sandhayak Class
INS Nirupak J14 - Sandhayak Class

INS Magar L20 - Magar Class (Amphibious Warfare Vessel)
INS Gharial L23 - Magar Class

INS Savitiri P53 - Sukanya Class (Large Patrol Craft)
INS Aditya A59 - Replenishment Tanker

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SOUTHERN NAVAL COMMAND, HQ - KOCHI (COCHIN)

1st Training Squadron @ Kochi
INS Tir A86
INS Krishna F46
INS Tarangini - Varuna Class (Sail Training Ship)

20th MCM Squadron @ Kochi - Inshore Minesweepers
INS Mahé M83 - Mahé Class
INS Malpe M86 - Mahé Class

Other Boats @ Kochi

INS Sharada P55 - Sukanya Class (Large Patrol Craft)
INS Sujata P56 - Sukanya Class

INS Jamuna J16 - Sandhayak Class (Survey Ship)
INS Sutlej J17 - Sandhayak Class

INS Sagardhwani A74 - Research Ship
INS Varuna - Sail Training Vessel

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ANDAMAN & NICOBAR COMMAND, HQ - PORT BLAIR

5th Landing Ship Squadron @ Port Blair
INS Sharabh L17 - Polnochny C Class (Amphibious Warfare Vessel)
INS Cheetah L18 - Polnochny D Class
INS Mahish L19 - Polnochny D Class
INS Guldar L20 - Polnochny D Class
INS Kumbhir L22 - Polnochny D Class

These may not all be currently active and reflect historical information.

• 4th Amphibious Squadron - 1st batch of Polnochny Class vessels which have now been decommissioned.

• 15th Frigate Squadron - Formerly equipped with Type 12 frigates, the old Talwar & Trishul.

• 16th Frigate Squadron - Formerly equipped with Type 41 frigates, the old Beas, Betwa & Brahmaputra.

• 21st Missile Vessel Squadron (K21) - Located at Mumbai and formerly equipped with Durg Class corvettes.

• 32nd Patrol Vessel Squadron - Used to be with Petya-II Class frigates.

• 149th MCM Squadron - Used to be equipped with Ton Class vessels.

• 239th MCM Squadron - Used to be equipped with Ham Class vessels.

• 321st Sea/Land Patrol Squadron.

• 322nd SDB Squadron.

• 324th SDB Squadron.