India's first indigenous warship INS Shivalik commissioned‎

It's a ship that is designed to escape detection by normal radars and surveillance equipment. Special aerodynamics, equipment and material used in designing and building these ships makes it very difficult to monitor their movements. That's why they are called 'stealth frigates.'

It's called the INS Shivalik, and it's the first ship built by India designed to escape detection by normal radars and surveillance equipment. India on Thursday stormed into an elite club of eight nations that build stealth warships with the commissioning of the first indigenous stealth frigate INS Shivalik, adding new fire power and muscle to its Navy.

Marking a 'red letter day' for the country, Defence Minister A K Antony launched the Rs 2,300 crore ship that has the capability to hoodwink enemy radars apart from having protection from nuclear-biological-chemical warfare.

"INS Shivalik's commissioning is a red letter day for the Indian Navy, armed forces, the government of India and the entire nation," Antony said, unveiling the pennant of the 6,200-tonne warship at the Mazagon Docks (MDL) here. Shivalik would be the first in the series of three frigates in this class.

Apart from India, only the US, Russia, UK, France, Sweden, Japan, Italy and China have the capability to build stealth warships of this size and class.

'Shivalik', which marks another move in securing India's sea lanes, is equipped with a judicious mix of imported and indigenous weapon systems and sensors, including Barak surface-to-air missiles and 'Shtil' air defence system. Antony said the indigenous content for the new frigate in terms of components was 80 per cent.

The MDL is building two other warships in this Shivalik series to be named INS Sayahdri and INS Satpura which would be commissioned by the end of this year and middle of next year respectively under Project-17. Seven more frigates would be built by the Defence PSU shipyard under a follow-on order, codenamed Project-17A very soon.

Antony said India's 7,500-km long coastline and maritime interests make it imperative to protect our mainland and also the sea lanes of communication. "With the commissioning of the frigate, I have no doubt our maritime interests are far more secure," he said. He said the security situation in and around India's neighbourhood posed many challenges and reiterated his call to the Navy to maintain high levels of operational readiness at all times.

He also referred, during his interaction with reporters, to the increased piracy in the Gulf of Aden,Seychelles and Mauritius seas to stress the need for a strong and potent navy to counter these threats. "In the coming years, protection of sea lanes is going to be a major challenge. So Indian Navy will have to perform its duty to protect our sea lanes," he said.

How Torpedos's are working under the water

Generally torpedos are used mainly in the war time. Its an under water weopen which is used to destroy enemys ships silently in the under water. Submarine ship will hold this weopen beside. During War time it will be used. in Torpedos front part will hold the homing device which is used to homing the sound of the enemies boat propeller. Wher ever the Enemy Ship will went it will search and destroy the ship silently..

A torpedo is essentially a guided missile that happens to "fly" underwater (see How Cruise Missiles Work for details on missiles). A torpedo therefore has a propulsion system, a guidance system and some sort of explosive device. Torpedoes can travel several miles on their way to the target, and therefore they need a propulsion system that can run for 10 to 20 minutes.

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Torpedoes either use batteries and an electric motor or a special kind of fuel to propel themselves.

Most missiles that fly through the air use either rocket engines or jet engines, but neither of these work very well underwater. Torpedoes use one of­ two techniques for propulsion:

• Batteries and an electric motor -- This is the same technique that any non-nuclear submarine must use when running underwater.
• Engines that use special fuel -- Most engines that we are familiar with, like car engines and jet engines, draw their oxygen from the air around the engine and use it to burn a fuel. A torpedo cannot do that, so it uses a fuel that either does not need an oxidizer, or it carries the oxidizer inside the torpedo. OTTO fuel (see the links below) has its own oxidizer mixed with the fuel. Hydrogen Peroxide (as discussed on this page) does not need an oxidizer.

We don't encounter too many fuels that contain their own oxidizers in our normal lives for two reasons. When a fuel has its own oxidizer it tends to make it explosive. Dynamite, for example, has its own oxidizer and it is quite explosive (see Question 397 for details on dynamite). Rocket engines have to carry their own oxidizer. But because we normally run engines in the air, which has a good supply of oxygen, carrying the oxidizer means extra weight and hassle which is unnecessary.

How Sailing Ships Works

Introduction:

Sailing began as a way to explore the world. While today's sailors still retain the bold spirit of explorers from centuries past, sailing is no longer a primary means of transportation and international trade or method of war. Since the 17th century, people have been setting sail for adventure and sport.

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Crew members on a racing yacht brace themselves to stay on the boat.

Most modern sailors sail because they love being on the water. Sailing is ranked as the 17th fastest-growing sport in the U.S., and it's estimated that more than 4 million Americans are recreational sailors [source: The Boating Channel]. The appeal of sailing is ageless: 40 percent of sailors are between the ages of 25 to 44, and roughly 17 percent are younger than age 17 [source: The Boating Channel].

So whether you're inspired by famous explorers such as Amerigo Vespucci or Vasco Da Gama, the winners of the America's Cup sailing races, or you just love the feel of wind in your hair, sailing is a sport to sate your adventurous side. Fair winds!

Types of Recreational Sailing

If you're looking for a little fun and some high-seas adventure, there are some popular types of recreational sailing that may suit you. If you're looking for something a little different, we have a few unconventional suggestions, too.

If you're a sailing novice, you might want to start out with small sailboats like dinghies, daysailers and small keelboats. They're easy to maneuver, are usually less than 25 feet in length. These can be sailed by an individual (solo sailing) or with one crewmember [source: U.S. Sailing]. Some sailors begin with small sailboats and continue adventuring this way even as they become experts. Dinghies are fun and lightweight -- they're used by college racing teams and in the Olympics, and they're perfect for weekend warriors.

Chris Jackson/Getty Images
A fleet of 50 Enterprise dinghies sails down the Thames past Chelsea Bridge and Battersea Power Station in London.

Some adventurers, though, take their sailing hobby to a whole new level and go cruising. Cruising isn't a just a hobby; it's a lifestyle. When you hear about someone who is sailing around the world, they're cruising. Sailors who choose cruising live on their sailboats and travel for extended periods of time. Their vessels range from basic keelboats to large, multi-hull cruising yachts. Most boats intended for cruising have many of the comforts of home below deck, and depending on their size, may include beds, bathrooms, kitchen facilities and even entertainment systems.

For those who want the adventure or relaxation of sailing without the work, boats can be chartered with skippers, and yachts can be chartered with crews. Two popular types of family-friendly chartered sailing adventures are sunset cruises and Caribbean sailing vacations. Sunset cruises are leisurely sailing experiences and are typically chartered by small groups looking to relax. If sailing in the Caribbean like the rich and famous sounds more like your style, boats (with or without hired crews) may be chartered through travel agencies. Some popular island destinations for Caribbean sailors include the Virgin Islands, Antigua, St. Barts, St. Martin and Grenada.

Basic Sailing Skills and Terms

The basics of sailing are easy to learn in a few classes, although it can take a lifetime to perfect them. Of the many skills and techniques to learn about sailing, there are five essentials: sail setting, boat balance, fore and aft trim, position of the centerboard, and course made good.

Ryan McVay/Allsport Concepts
The crew members of a racing yacht are sure to know the five basics of sailing.

1. Sail setting: Sailboats can't be taken directly into the wind or they run the risk of stopping (when there's literally no wind in your sails). Depending on your point of sail -- the direction of your boat in relation to the direction of the wind -- different sail settings are needed. You can set your main sail by listening to it: Ease the sail out until it flaps along the luff, the part closest to the mast, and then pull it back in just until the flapping stops.

2. Boat balance: When your boat begins to lean to one side, it's known as heeling. To overcome heeling and stay on course, it's important to stay aware of the wind (is it gusting?) and the position of your sails. Also keep aware of the weight you have onboard and how it's distributed. If your boat is leaning port side, you can counteract it by moving your weight (or the weight of the crew) to the opposite, or starboard, side.

3. Fore and aft trim: A boat must also stay balanced from end-to-end. Generally, the front of a boat (bow) is raised slightly higher than the back (stern), and the distribution of body weight on board (you and your crew) is key to maintaining that balance. If you find your boat is dragging in the water (an example of what happens when the back of the boat is too low), move your weight closer to the middle or front of the boat. If the bow is submerging in the water, take a seat toward the back of the boat. A correctly balanced boat allows you to sail more quickly.

4. Position of the centerboard: There is a delicate balance between your boat and the wind, and you can easily find yourself being pushed off course by it. The centerboard, a piece of wood, fiberglass or metal (depending on what your boat is made from), is a movable fin under the hull. By adjusting it in relation to your point of sail, you're able to correct any drift.

5. Course made good: Getting from point A to point B isn't always a straight course, especially if the straight course takes you directly into the wind. Planning a route that gets you to your destination in the shortest possible time is called "course made good." This is generally accomplished through a maneuver called tacking, in which the boat is steered in a zigzag, upwind direction.

To find a sailing school in the United States, visit the American Sailing Association.

Knot Knowledge
Sailors know their knots. There are two general types you should know: bend and hitch. A bend is a knot that fastens rope ends together. A hitch loops a rope around itself to secure the boat to a rail or post.

There are hundreds of knots but only a few basics that should be on your practice list:

• Bowline: A bowline knot is your standby. It creates a loop at the end of a top, is strong and easy to untie. If you know the old saying, the rabbit comes out of his hole, 'round the tree and back down into his hole, you already know the bowline. When in doubt, use this knot.
• Square knot: The square knot, or reef knot, is used to tie two ropes (lines) of the same size together. You may be familiar with it from Boy Scouts or Girl Scouts, first-aid class or from tying your shoelaces.
• Clove hitch: This loop is a quick way to temporarily moor a small boat to a ring, rail or post.
• ­Round turn and two half hitches: This knot is frequently used to secure a boat to the docking ring or post.
• Figure-of-eight: This stopper knot is used to prevent a rope from unraveling or slipping out of a ring or other device. This type of knot is essential in both sailing and rock climbing.
• Sheet bend: Need a longer rope? A sheet bend knot is a quick way to fasten two lines temporarily.

  Sailing Safety and Regulations

  To keep recreational sailing a fun and safe activity, there are some rules sailors are expected to follow. First, it's important to be honest about your skill level. Don't overextend yourself -- if you're a beginner or an old pro, going beyond your skill puts both you and others at risk. According to the U.S. Coast Guard, 70 percent of reported deaths at sea occur because the boat operator didn't have adequate (or any) boating instruction [source: U.S. Coast Guard].

  
  Peter Mumford/Beken/Kos Picture Source via Getty Images
  Sailors need to pay attention to the weather forecast so they don't get caught in a sudden squall. These yachts are competing in the J109 UK National Championships.

  Your skills will only take you so far -- you'll need wind in your sails to get you out on the water. Make sure to determine the wind speed and direction before you set out. Also check the forecast. It may be sunny as you make your preparations, but a change in the weather could result in a dangerous expedition.

  Sailboat Racing As their sailing skills improve, many sailors enjoy testing their techniques, strategies and tactics in races. Races are organized by sailing clubs and schools around the world. There are two types of sailboat races: team racing (or fleet racing) where two to four boats compete together, and match racing, where two boats compete head to head. One of the most famous two-boat races is the America's Cup, in which the best sailors, engineers and boat builders get to show off their skills. The rules -- known as the Racing Rules of Sailing -- are established by the International Sailing Federation (ISAF) and are published every four years. Visit the ISAF to download a copy of the Racing Rules of Sailing.

  With skill level and wind direction determined, you'll also want to inspect your boat, gear and tools to ensure they're all in good condition, and note if you have everything you need onboard before setting out. Federal law requires you to carry safety equipment onboard. You and your crew should wear life jackets and all know how to use the boat's safety equipment. Be sure to know how to make a distress call for immediate assistance -- the time you find yourself in trouble is not the time to figure how to call for help.

  It's also smart to have a plan. On your adventure you'll likely be out of sight of land, and if you have an emergency, it might be difficult for help to find you. Put together a float plan and leave a copy with a friend or local marina before you set sail. At the least, your plan should include:

• A description of your boat
• The name of your boat operator and the names of all people onboard
• What type of safety and survival equipment you have with you (food, flares, paddles, marine radios, etc.)
• Your destination, arrival and departure times

Skill, wind, inspection and a plan -- check. Once you've launched your boat, be alert and aware of your surroundings. By simply maintaining a safe speed and looking around you, you're less likely to collide with other boats or objects (the top two causes of accidents [source: U.S. Coast Guard]). And leave the alcohol on shore: Drinking and operating equipment is just as dangerous at sea as it is on the roads. Violators with a blood alcohol content of .08 percent or higher may be subject to civil and criminal penalties, one year imprisonment or both. [source: U.S. Coast Guard]. Alcohol use is a leading factor in fatal boating accidents -- nearly 20 percent of reported fatalities [source: U.S. Coast Guard].

For a comprehensive list of rules and regulations, visit the U.S. Coast Guard's Navigation Center.

Boating Superstitions

If you're smart and follow basic sailing regulations, you should be able to stay safe on your expedition. But sailors are a superstitious bunch and have many nautical myths:

• Whistling: It's a universal sailing superstition that whistling onboard will surely whip up the winds, thus the saying "whistling up a storm."
• Earrings: Some sailors believe they cannot drown if they wear earrings.
• Lefties: It's said sailors would never step on or off a boat leading with the left foot, fearing bad luck. This is a type of sinistrophobia, the fear of things on the left side of the body, and of south-paws.
• Animals: Superstitions surrounding animals abound. Black cats are good omens, as are dolphins. But watch out for sharks; they're rumored to spell doom.
• The Flying Dutchman: The Flying Dutchman is a ghost ship, and as legend goes, its appearance signals imminent danger or death to those who see it.

­

How Aircraft Carrier works

Introduction:
When the U.S. Navy really needs to impress people, it flies them out to one of its super aircraft carriers. Standing 20 stories above the water and stretching 1,092 feet (333 meters) from bow to stern (about as long as the 77-story Chrysler Building is tall), the sheer bulk of these ships is awe-inspiring. But the really amazing thing about a supercarrier isn't its size; it's the intense scene on its flight deck. When the crew is in full swing, it can launch or land a plane every 25 seconds -- all in a fraction of the space available on a typical landing strip.
In this article,we'll find out what the U.S. Navy's modern Nimitz-class aircraft carriers are all about. We'll learn what's on the different decks, take a look at the amazing machines that help launch and land aircraft, and find out a little about daily life on these enormous floating bases. As we'll see, the modern aircraft carrier is one of the most amazing vehicles ever created.


Photo courtesy U.S. Dept. of Defense
The USS Nimitz, one of the U.S. Navy's super aircraft carriers. See more pictures of aircraft carriers.



At its most basic level, an aircraft carrier is simply a ship outfitted with a flight deck -- a runway area for launching and landing airplanes. This concept dates back almost as far as airplanes themselves. Within 10 years of the Wright Brothers' historic 1903 flight, the United States, the United Kingdom and Germany were launching test flights from platforms attached to cruisers. The experiments proved largely successful, and the various naval forces started adapting existing warships for this purpose. The new carriers allowed military forces to transport short-range aircraft all over the world.

Photo courtesy U.S. Department of Defense
The USS George Washington, one of the U.S. Navy's nuclear-powered super aircraft carriers

Carriers didn't play a huge role in World War I, but they were central to the air combat of World War II. For example, the Japanese launched the 1941 attack on Pearl Harbor from aircraft carriers. Today, super aircraft carriers are a crucial part of almost all major U.S. military operations. While the ship itself isn't especially useful as a weapon, the air power it transports can make the difference between victory and defeat.

One of the major obstacles of using air power in war is getting the planes to their destination. To maintain an air base in a foreign region, the United States (or any other nation) has to make special arrangements with a host country, and then has to abide by that country's rules, which may change over time. Needless to say, this can be extremely difficult in some parts of the world.

Under international Freedom of Navigation laws, aircraft carriers and other warships are recognized as sovereign territories in almost all of the ocean. As long as a ship doesn't get too close to any nation's coast, the crew can carry on just like they're back home. So, while the U.S. military would have to make special arrangements with a foreign nation to set up a land military base, it can freely move a carrier battle group (an assembly of an aircraft carrier and six to eight other warships) all over the globe, just as if it were a little piece of the United States. Bombers, fighters and other aircraft can fly a variety of missions into enemy territory, and then return to the relatively safe home base of the carrier group. In most cases, the Navy can continually replenish (resupply) the carrier group, allowing it to maintain its position indefinitely.

Carriers can move in excess of 35 knots (40 mph, 64 kph), which gives them the ability to get anywhere in the ocean in a few weeks. The United States currently has six carrier groups stationed around the world, ready to move into action at a moment's notice.

Talking the Talk Ships have their own special language, particularly when it comes to getting from point to point. Here's a quick primer, in case you don't know aft from bow.

• Stern - the rear of the ship
• Bow - the front of the ship
• Starboard - the right side of the ship (if you're facing the bow)
• Port - the left side of the ship
• Forward - moving toward the bow of the ship (as in, "Moving forward on the flight deck" or "The hangar deck is forward of the fantail.")
• Aft - moving toward the stern of the ship
• Inboard - moving from the side of the ship toward the center of the ship
• Outboard - moving from the center of the ship to the side of the ship
• Below - on a lower deck (as in, "Going below to the hangar" -- You never "go downstairs" on a ship, you always "go below.")
• Fantail - the stern area of the main deck (the hangar deck on a carrier) .
  
  THE PARTS OF AN AIRCRAFT CARRIER:
• With about a billion individual pieces, the U.S. Nimitz-class supercarriers are among the most complex machines on earth. But on a conceptual level, they're pretty simple. They're designed to do four basic jobs:

  • Transport a variety of aircraft overseas
  • Launch and land airplanes
  • Serve as a mobile command center for military operations
  • House all the people who do these things

  To accomplish these tasks, a carrier needs to combine elements of a ship, an air force base, and a small city. Among other things, it needs:

  • A flight deck, a flat surface on the top of the ship where aircraft can take off and land
  • A hangar deck, an area below deck to stow aircraft when not in use
  • An island, a building on top of the flight deck where officers can direct flight and ship operations
  • Room for the crew to live and work
  • A power plant and propulsion system to move the boat from point to point and to generate electricity for the entire ship
  • Various other systems to provide food and fresh water and to handle things that any city has to deal with, like sewage, trash and mail, as well as carrier-based radio and television stations and newspapers
  • The hull, the main body of the ship, which floats in water

  The diagrams below show how these various components fit together.

  Cutaway view

  Top view

  The hull of the ship is made up of extremely strong steel plates, measuring several inches thick. This heavy body is highly effective protection against fire and battle damage. The ship's structural support largely comes from three horizontal structures extending across the entire hull: the keel (the iron backbone on the bottom of the ship), the flight deck and the hangar deck.

  The hull portion below the water line is rounded and relatively narrow, while the section above water flares out to form the wide flight-deck space. The lower section of the ship has a double bottom, which is pretty much what it sounds like -- there are two layers of steel plating: the bottom plating of the ship and another layer above it, separated by a gap. The double bottom provides extra protection from torpedos or accidents at sea. If the enemy hits the bottom of the ship, smashing a hole in the outer steel layer, the second layer will prevent a massive leak.

  Building an Aircraft Carrier

  Since the 1950s, almost all U.S. supercarriers have been constructed at Northrop Grumman Newport News in Newport News, Virginia. To make the construction process more efficient, most of each supercarrier is assembled in separate modular pieces called superlifts. Each superlift may contain many compartments (rooms), spanning multiple decks, and they can weigh anywhere from 80 to 900 tons (~70 to 800 metric tons). A supercarrier is made up of almost 200 separate superlifts.

  Photo courtesy Northrop Grumman Newport News

  Photo courtesy Northrop Grumman Newport News The USS Ronald Reagan, under construction in the Northrop Grumman Newport News dry dock

  Before placing a superlift module into the ship, the construction crew assembles its steel body and hooks up almost all wiring and plumbing. Then they use a giant bridge crane to lift the module and lower it precisely into its proper position inside the ship; then they weld it to the surrounding modules. Near the end of construction, the crew joins the last module, the 575-ton island, to the flight deck.

  Photo courtesy U.S. Navy

  Photo courtesy U.S. Navy Lowering superlifts into position on the USS Harry S. Truman

  Just like the family motor boat, an aircraft carrier propels itself through the water by spinning propellers. Of course, at about 21 feet (6.4 meters) across, a carrier's four bronze screw propellers are in a very different league than a recreational boat's. They also have a lot more power behind them. Each propeller is mounted to a long shaft, which is connected to a steam turbine powered by a nuclear reactor.

  The carrier's two nuclear reactors, housed in a heavily-armored, heavily restricted area in the middle of the ship, generate loads of high-pressure steam to rotate fan blades inside the turbine. The fans turn the turbine shaft, which rotates the screw propellers to push the ship forward, while massive rudders steer the ship. The propulsion system boasts something in excess of 280,000 horsepower (the Navy doesn't release exact numbers).

  The four onboard turbines also generate electricity to power the ship's various electric and electronic systems. This includes an onboard desalination plant that can turn 400,000 gallons (~1,500,000 liters) of saltwater into drinkable freshwater every day -- that's enough for 2,000 homes.

  Unlike the old oil-boiler carriers, modern nuclear carriers don't have to refuel regularly. In fact, they can go 15 to 20 years without refueling. The trade-offs are a more expensive power plant, a longer, more complicated refueling process (it takes several years) and the added risk of a nuclear disaster at sea. To minimize the risk of such a catastrophe, the reactors inside a supercarrier are heavily shielded and closely monitored.

  Big Numbers These stats paint a nice picture of the scope of a Nimitz-class aircraft carrier.

  From the USS Theodore Roosevelt Web site:

  • Total height, from keel to mast - 244 feet (~74 meters), as high as a 24 story building.
  • Fully loaded displacement (the weight of water displaced by the ship when in full combat mode) - 97,000 tons (~88,000 metric tons)
  • Weight of structural steel - 60,000 tons (~54,000 metric tons)
  • Total area of flight deck - 4.5 acres (~1.8 hectares)
  • Length of flight deck - 1,092 feet (~333 meters)
  • Width of flight deck (at the widest point) - 257 feet (~78 meters)
  • Number of compartments and spaces onboard - 4,000+
  • Weight of each anchor - 30 tons (~27 metric tons)
  • Weight of each link in the anchor chains - 360 pounds (~160 kg)
  • Weight of each propeller - 66,200 pounds (~30,000 kg)
  • Weight of each rudder - 45.5 tons (~41 metric tons)
  • Storage capacity for aviation fuel - 3.3 million gallons (~12.5 million liters)
  • Number of telephones onboard - 2,500+
  • Number of televisions onboard - 3,000+
  • Total length of electrical cable onboard - 1,000+ miles (1,600+ km)
  • Air conditioning plant capacity - 2,250 tons (~2,040 metric tons, enough to cool more than 500 houses)

  From the USS Nimitz Web site:

  • Storage capacity for refrigerated and dried food: enough to feed 6,000 people for 70 days.
  • Mail processed every year by onboard post office - 1 million pounds (~450,000 kg)
  • Number of dentists - 5
  • Number of medical doctors - 6
  • Beds in hospital ward - 53
  • Number of chaplains in interdenominational chapel - 3
  • Number of haircuts every week - 1,500+
  • Number of barbershops - 1

    Taking Off from an Aircraft Carrier

    An aircraft carrier flight deck is one of the most exhilarating and dangerous work environments in the world (not to mention one of the loudest). The deck may look like an ordinary land runway, but it works very differently, due to its smaller size. When the crew is in full swing, planes are landing and taking off at a furious rate in a limited space. One careless moment, and a fighter jet engine could suck somebody in or blast somebody off the edge of the deck into the ocean.

    But as dangerous as the flight deck is for the deck crew, they have it pretty easy compared to the pilots. The flight deck isn't nearly long enough for most military planes to make ordinary landings or takeoffs, so they have to head out and come in with some extraordinary machine assistance.

    Photo courtesy U.S Department of Defense An A-6E Intruder launches from the USS George Washington.

    If you've read How Airplanes Work, you know that an airplane has to get a lot of air moving over its wings to generate lift. To make takeoff a little easier, carriers can get additional airflow over the flight deck by speeding through the ocean, into the wind, in the direction of takeoff. This air moving over the wings lowers the plane's minimum takeoff speed.

    Getting air moving over the deck is important, but the primary takeoff assistance comes from the carrier's four catapults, which get the planes up to high speeds in a very short distance. Each catapult consists of two pistons that sit inside two parallel cylinders, each about as long as a football field, positioned under the deck. The pistons each have a metal lug on their tip, which protrudes through a narrow gap along the top of each cylinder. The two lugs extend through rubber flanges, which seal the cylinders, and through a gap in the flight deck, where they attach to a small shuttle.

    Photo courtesy U.S Department of Defense The shuttle of catapult number four on USS John Stennis

    To prepare for a takeoff, the flight deck crew moves the plane into position at the rear of the catapult and attaches the towbar on the plane's nose gear (front wheels) to a slot in the shuttle. The crew positions another bar, the holdback, between the back of the wheel and the shuttle (in F-14 and F/A-18 fighter jets, the holdback is built into the nose gear; in other planes, it's a separate piece).

    Photo courtesy U.S Navy A member of the USS George Washington flight-deck crew checks an F-14 Tomcat's catapult attachment.

    While all of this is going on, the flight crew raises the jet blast deflector (JBD) behind the plane (aft of the plane, in this case). When the JBD, towbar and holdback are all in position, and all the final checks have been made, the catapult officer (also known as the "shooter") gets the catapults ready from the catapult control pod, a small, encased control station with a transparent dome that protrudes above the flight deck.

    Photo courtesy U.S Department of Defense Steam rises from the catapult as an F/A-18C Hornet prepares to launch from the USS George Washington. You can see the catapult officer in the catapult control pod.

    Photo courtesy U.S Department of Defense An F-14 Tomcat, positioned in front of the jet blast deflector on USS Nimitz's catapult number 1

    When the plane is ready to go, the catapult officer opens valves to fill the catapult cylinders with high-pressure steam from the ship's reactors. This steam provides the necessary force to propel the pistons at high speed, slinging the plane forward to generate the necessary lift for takeoff. Initially, the pistons are locked into place, so the cylinders simply build up pressure. The catapult officer carefully monitors the pressure level so it's just right for the particular plane and deck conditions. If the pressure is too low, the plane won't get moving fast enough to take off, and the catapult will throw it into the ocean. If there's too much pressure, the sudden jerk could break the nose gear right off.

    When the cylinders are charged to the appropriate pressure level, the pilot blasts the plane's engines. The holdback keeps the plane on the shuttle while the engines generate considerable thrust. The catapult officer releases the pistons, the force causes the holdbacks to release, and the steam pressure slams the shuttle and plane forward. At the end of the catapult, the tow bar pops out of the shuttle, releasing the plane. This totally steam-driven system can rocket a 45,000-pound plane from 0 to 165 miles per hour (a 20,000-kg plane from 0 to 266 kph) in two seconds!

    Photo courtesy U.S Department of Defense An F/A-18 Hornet launching from the USS George Washington

    If everything goes well, the speeding plane has generated enough lift to take off. If not, the pilot (or pilots) activate their ejector seats to escape before the plane goes hurdling into the ocean ahead of the ship (this hardly ever happens, but the risk is always there).

    Taking off is extremely difficult, but the real trick is coming back in.

    Landing on an Aircraft Carrier

    Landing on a flight deck is one of the most difficult things a navy pilot will ever do. The flight deck only has about 500 feet (~150 meters) of runway space for landing planes, which isn't nearly enough for the heavy, high-speed jets on U.S. carriers.

    To land on the flight deck, each plane needs a tailhook, which is exactly what it sounds like -- an extended hook attached to the plane's tail. The pilot's goal is to snag the tailhook on one of four arresting wires, sturdy cables woven from high-tensile steel wire.

    Photo courtesy U.S Department of Defense An ES-3A Shadow comes in for a landing aboard the USS George Washington.

    The arresting wires are stretched across the deck and are attached on both ends to hydraulic cylinders below deck. If the tailhook snags an arresting wire, it pulls the wire out, and the hydraulic cylinder system absorbs the energy to bring the plane to a stop. The arresting wire system can stop a 54,000-pound aircraft travelling 150 miles per hour in only two seconds, in a 315-foot landing area (a 24,500-kg aircraft travelling at 241 kph in a 96-meter landing area).

    Photo courtesy U.S Department of Defense The tailhook of a KA-6D Intruder aircraft, about to catch an arresting wire on the USS Dwight D. Eisenhower

    Photo courtesy U.S Department of Defense An F/A-18C Hornet catches an arresting wire on the USS Nimitz.

    There are four parallel arresting wires, spaced about 50 feet (15 meters) apart, to expand the target area for the pilot. Pilots are aiming for the third wire, as it's the safest and most effective target. They never shoot for the first wire because it's dangerously close to the edge of deck. If they come in too low on the first wire, they could easily crash into the stern of the ship. It's acceptable to snag the second or fourth wire, but for a pilot to move up through the ranks, he or she has to be able to catch the third wire consistently.

    To pull off this incredible trick, the pilot needs to approach the deck at exactly the right angle. The landing procedure starts when the various returning planes "stack up" in a huge oval flying pattern near the carrier. The Carrier Air Traffic Control Center below deck decides the landing order of the waiting planes based on their various fuel levels (a plane that's about to run out of fuel comes down before one that can keep flying for a while). When it's time for a plane to land, the pilot breaks free of this landing pattern and heads toward the stern of the ship.

    Landing Signals Officers (LSOs) help guide the plane in, through radio communication as well as a collection of lights on the deck. If the plane is off course, the LSOs can use radio commands or illuminate other lights to correct him or her or "wave him off" (send him around for another attempt).

    Photo courtesy U.S Department of Defense The Landing Signals Officers guide a landing aircraft on the USS George Washington.

    Photo courtesy U.S Department of Defense The video display console and communications/data board at the Landing Signals Officers' work station

    In addition to the LSOs, pilots look to the Fresnel Lens Optical Landing System, commonly referred to as the lens, for landing guidance. The lens consists of a series of lights and Fresnel lenses mounted to a gyroscopically stabilized platform. The lenses focus the light into narrow beams that are directed into the sky at various angles.

    The pilot will see different lights depending on the plane's angle of approach. If the plane is right on target, the pilot will see an amber light, dubbed the "meatball," in line with a row of green lights. If the amber light appears above the green lights, the plane is coming in too high; if the amber light appears below the green lights, the plane is coming in too low. If the plane is coming in way too low, the pilot will see red lights.

    Photo courtesy U.S. Department of Defense "The lens" on the USS John F. Kennedy

    Photo courtesy U.S. Navy A diagram illustrating the "Long-Range Lineup System (LRLS)."

    As soon as the plane hits the deck, the pilot will push the engines to full power, instead of slowing down, to bring the plane to a stop. This may seem counterintuitive, but if the tailhook doesn't catch any of the arresting wires, the plane needs to be moving fast enough to take off again and come around for another pass. The landing runway is tilted at a 14-degree angle to the rest of the ship, so bolters like this can take off from the side of the ship instead of plowing into the planes on the other end of the deck.

    As soon as an aircraft lands, it's pulled out of the landing strip and chained down on the side of the flight deck. Inactive aircraft are always tightly secured to keep them from sliding around as the deck rocks back and forth.

    The flight-deck crew has to be prepared for a wide range of unexpected events, including raging aircraft fires. During takeoff or recovery operations, they have plenty of safety equipment at the ready. Among other things, the flight deck has a small fire truck, and nozzles leading to water tanks and aqueous film-forming foam, an advanced fire-extinguishing material (there are also nozzles for jet fuel and a number of other useful liquids).

    Photo courtesy U.S Department of Defense An S-3A Viking aircraft lands on the USS Abraham Lincoln with the help of the crash barricade. The plane had to make an unconventional landing due to a problem with its landing gear.

    Flight-deck personnel also face the risk of a jet engine blowing them overboard. Safety nets around the side of the flight deck offer some protection, but for extra safety, personnel are also equipped with float coats, self-inflating jackets with flashing distress lights, activated by contact with water. Flight-deck personnel also wear heavy-duty helmets, called cranials, which protect their head and their hearing.

    The Island

    An aircraft carrier's "island" is the command center for flight-deck operations, as well as the ship as a whole. The island is about 150 feet (46 m) tall, but it's only 20 feet (6 m) wide at the base, so it won't take up too much space on the flight deck. The top of the island, well above the height of any aircraft on the flight deck, is spread out to provide more room.

    Photo courtesy U.S Department of Defense The island on the USS Abraham Lincoln

    The top of the island is outfitted with an array of radar and communications antennas, which keep tabs on surrounding ships and aircraft, intercept and jam enemy radar signals, target enemy aircraft and missiles and pick up satellite phone and TV signals, among other things. Below that is the Primary Flight Control, or Pri-Fly. In the Pri-Fly, the air officer and air officer assistant (known as the "Air Boss" and the "Mini Boss") direct all aircraft activity on the flight deck and within a 5-mile (8-km) radius.

    Photo courtesy U.S Department of Defense The busy scene in the Pri-Fly

    The Air Boss and Mini-Boss, both experienced aviators, have an array of computers and communications equipment to keep tabs on everything, but they get a lot of information just by looking out their windows, six stories above the flight deck. When an approaching plane gets within three-quarters of a mile (1.2 km), the Landing Signals Officers take over control to direct the landing procedure. At the same level as the Pri-Fly, crew and visitors can walk out onto vulture's row, a balcony platform with a great view of the entire flight deck.

    The next level down is the bridge, the ship's command center. The commanding officer (the captain) usually cons (controls) this ship from a stately leather chair surrounded by computer screens. The commanding officer directs the helmsman, who actually steers the carrier, the lee helmsman, who directs the engine room to control the speed of the ship, the Quartermaster of the Watch, who keeps track of navigation information, and a number of lookouts and support personnel. When the commanding officer is not on the bridge, he puts an Officer of the Deck in charge of operations.

    Photo courtesy U.S Department of Defense Captain David Logsdon commands the USS Harry Truman from the flight deck.

    Photo courtesy U.S Department of Defense The lee helmsman (left) and helmsman on the USS Theodore Roosevelt

    Interestingly enough, many carrier commanding officers are former Navy airplane pilots, so they have a personal understanding of flight-deck operations. As long as they're in command of a carrier, however, they're prohibited from climbing into the cockpit to fly a plane themselves.

    Just like the Pri-Fly, the bridge is outfitted with an array of high-end monitors, including GPS receivers and many radar screens. But the commanding officer and his team still rely heavily on their own eyes to keep tabs on activity around the ship.

    The level below the bridge is the flag bridge, the command center for the admiral in charge of the entire carrier group. Below that, there are various operational centers, including the flight deck control and launch operations room. In this tight, windowless space, the aircraft handling officer (also called the handler or mangler) and his or her crew keep track of all the aircraft on the flight deck and in the hangar. The handler's primary tracking tool is the "Ouija Board," a two-level transparent plastic table with etched outlines of the flight deck and hangar deck. Each aircraft is represented by a scale aircraft cut-out on the table. When a real plane moves from point to point, the handler moves the model plane accordingly. When the plane is out of service, because it needs repair work, the handler turns it over.

    Photo courtesy U.S Department of Defense Crew members on the USS George Washington circle around the "Ouija Board."

    There are a number of additional control centers below deck, including the carrier air traffic control center (CATCC), which takes up several rooms on the galley deck (immediately below the flight deck). Like a land-based air traffic control center, the CATCC is filled with all sorts of radio and radar equipment, which the controllers use to keep track of aircraft in the area (in this case, mainly the aircraft outside the Air Boss's supervision).

    The CATCC is next to the combat direction center (CDC), the ship's battle command center. The CDC's primary responsibility is to process incoming information on enemy threats in order to keep the commanding officer fully informed.

    Photo courtesy U.S Department of Defense An air traffic controller onboard the USS Kitty Hawk

    
    Photo courtesy U.S Department of Defense
    An antisubmarine warfare specialist on the USS Carl Vinson monitors activities in the Persian Gulf.

How Aircraft Carrrier works

Introduction:
When the U.S. Navy really needs to impress people, it flies them out to one of its super aircraft carriers. Standing 20 stories above the water and stretching 1,092 feet (333 meters) from bow to stern (about as long as the 77-story Chrysler Building is tall), the sheer bulk of these ships is awe-inspiring. But the really amazing thing about a supercarrier isn't its size; it's the intense scene on its flight deck. When the crew is in full swing, it can launch or land a plane every 25 seconds -- all in a fraction of the space available on a typical landing strip.
In this article,we'll find out what the U.S. Navy's modern Nimitz-class aircraft carriers are all about. We'll learn what's on the different decks, take a look at the amazing machines that help launch and land aircraft, and find out a little about daily life on these enormous floating bases. As we'll see, the modern aircraft carrier is one of the most amazing vehicles ever created.


Photo courtesy U.S. Dept. of Defense
The USS Nimitz, one of the U.S. Navy's super aircraft carriers. See more pictures of aircraft carriers.



At its most basic level, an aircraft carrier is simply a ship outfitted with a flight deck -- a runway area for launching and landing airplanes. This concept dates back almost as far as airplanes themselves. Within 10 years of the Wright Brothers' historic 1903 flight, the United States, the United Kingdom and Germany were launching test flights from platforms attached to cruisers. The experiments proved largely successful, and the various naval forces started adapting existing warships for this purpose. The new carriers allowed military forces to transport short-range aircraft all over the world.

Photo courtesy U.S. Department of Defense
The USS George Washington, one of the U.S. Navy's nuclear-powered super aircraft carriers

Carriers didn't play a huge role in World War I, but they were central to the air combat of World War II. For example, the Japanese launched the 1941 attack on Pearl Harbor from aircraft carriers. Today, super aircraft carriers are a crucial part of almost all major U.S. military operations. While the ship itself isn't especially useful as a weapon, the air power it transports can make the difference between victory and defeat.

One of the major obstacles of using air power in war is getting the planes to their destination. To maintain an air base in a foreign region, the United States (or any other nation) has to make special arrangements with a host country, and then has to abide by that country's rules, which may change over time. Needless to say, this can be extremely difficult in some parts of the world.

Under international Freedom of Navigation laws, aircraft carriers and other warships are recognized as sovereign territories in almost all of the ocean. As long as a ship doesn't get too close to any nation's coast, the crew can carry on just like they're back home. So, while the U.S. military would have to make special arrangements with a foreign nation to set up a land military base, it can freely move a carrier battle group (an assembly of an aircraft carrier and six to eight other warships) all over the globe, just as if it were a little piece of the United States. Bombers, fighters and other aircraft can fly a variety of missions into enemy territory, and then return to the relatively safe home base of the carrier group. In most cases, the Navy can continually replenish (resupply) the carrier group, allowing it to maintain its position indefinitely.

Carriers can move in excess of 35 knots (40 mph, 64 kph), which gives them the ability to get anywhere in the ocean in a few weeks. The United States currently has six carrier groups stationed around the world, ready to move into action at a moment's notice.

Talking the Talk Ships have their own special language, particularly when it comes to getting from point to point. Here's a quick primer, in case you don't know aft from bow.

• Stern - the rear of the ship
• Bow - the front of the ship
• Starboard - the right side of the ship (if you're facing the bow)
• Port - the left side of the ship
• Forward - moving toward the bow of the ship (as in, "Moving forward on the flight deck" or "The hangar deck is forward of the fantail.")
• Aft - moving toward the stern of the ship
• Inboard - moving from the side of the ship toward the center of the ship
• Outboard - moving from the center of the ship to the side of the ship
• Below - on a lower deck (as in, "Going below to the hangar" -- You never "go downstairs" on a ship, you always "go below.")
• Fantail - the stern area of the main deck (the hangar deck on a carrier)

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.