How Nuclear Submarines Work

Leonardo da Vinci sketched a primitive submarine around 1515, and in 1578, William Bourne drafted the first design for a submersible craft. In 1620, the first successful submarine was built by Cornelius Drebbel and tested in the Thames River, where it completed a three-hour journey.

At­ least 14 different submarine designs were patented by 1727 [source: Brittanica]. Early designs usually incorporated wooden submarine frames covered in oil-soaked waterproof leather, with oars extending from the hull for propulsion.­

­American inventor David Bushnell developed the first military submarine in 1775, during the American Revolution. The Turtle was used on July 7, 1776, to sneak up on a British battleship and attach an explosive device to the hull of the enemy ship. Ultimately, the Turtle's mission failed. Designing an underwater weapon delivery system proved to be a difficult task for years to come.

­Early subs were usually propelled by hand-operated cranks, and their offensive strategies centered around covertly confronting a surface ship, attaching explosives to the enemy's hull and escaping before the explosion. Though it may sound simple, the process was quite difficult. Many submarines were simply unable to catch up to enemy warships. Attaching explosives also proved tricky since it was difficult to penetrate the ships' hulls using screw-type devices.

By the War of 1812, a submarine similar to the Turtle had almost perfected this part. It was able to screw an appendage (a vertically aligned large screw to which a rope connected an explosive) into the hull of a British warship. But the screw dislodged, separating the torpedo from its intended target.

If able to catch up to an enemy ship and attach explosives to it, escaping proved just as difficult. The crew of the H.L. Hunley, a submarine used by the Confederacy during the Civil War, discovered this. The H.L. Hunley used a long spar, or arm, to hold and release an explosive charge, successfully sinking the USS Housatonic. However, the H.L. Hunley also fell victim to the ­explosion, and its entire crew died on Feb. 17, 1864.

On the next page, read about the other developments in submarine design that emerged later in the 19th century.­

Designs for a battery- and diesel-propelled submarine emerged in the years following the Civil War. In 1867, an important step was made with the successful launch of the world's first steam-powered submarine, the Ictineo II, created by Spain's Narcis Monturiol [source: Holian]. This development is notable because nuclear submarines are essentially steam-powered. (As we'll learn later, the main difference is that in nuclear submarines, the steam is created by superheating water using atomic fission. By contrast, in conventional steam engines, the power is created by burning coal.)

Before World War I, the United States focused its submarine fleet on coastal defense. The groundwork for the submarine race was laid at the turn of the century, as many features of future submarines were already in use. Engineers continued to tweak the designs of propellers, devised new systems for using water as ballast and the made strides toward the development of diesel-electric hybrid submarines. These subs were propelled on the surface using the diesel engine, and they went electric when submerged underwater. This combination saved valuable oxygen underwater and helped maintain the integrity of the air inside the submarine.

The United States realized that its submarine designs didn't compare favorably to those of other World War I combatants. In the decades between the World Wars, the U.S. reinvested in research and development, greatly improving the quality ­of its submarine fleet. One of the biggest improvements to U.S. submarines was that they were enabled to move at faster speeds that allowed them to accompany and protect naval fleets as they traveled across the world. The long-range fleet of U.S. submarines would later be responsible for bringing destruction to the Japanese fleet in the Pacific theater of war.

After World War II, both the U.S. and the Soviet Union studied the designs of the superior Nazi U-boats and altered their own submarines to mimic the U-boat. U-boats had a streamlined hull, which made them run faster than U.S. and USSR subs. They also utilized a snorkel, which was basically two tubes running between the submerged vessel and the surface. One tube brought air to the diesel engine and the other took foul air away. This allowed the submarine to remain submerged, even while the diesel engine was running.

In this postwar period, more streamlined and efficient diesel-electric subs emerged. Because of their low construction costs and stealthy silence, variants of those diesel-electric subs are still in use by navies worldwide today.

The U.S. Navy, however, was cooking up a bigger, bolder idea that would change naval strategy and tactics forever. You'll learn all about it in the next section­.

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The United States developed the world's first nuclear-powered submarine: the Nautilus. Its first nuclear-powered journey took place on Jan. 21, 1954. In contrast to the diesel-electric subs that preceded it (and are still in service around the world today), the Nautilus had a practically unlimited range. What's more, it could stay underwater for great lengths of time because it didn't have to surface to recharge electric batteries. And while most submarines were designed to travel primarily on the surface and dive on occasion, the Nautilus was designed to remain underwater and only surface on occasion.

The incredible range and maneuverability of nuclear submarines radically altered naval strategy and tactics. While submarines previously were maintained for coastal defense, this new breed of submarine could -- and did -- travel the globe. Just a few years after being put to sea, the Nautilus became the first submarine to sail beneath the arctic ice, reaching the North Pole on Aug. 3, 1958. After it reached the North Pole, the Nautilus was overhauled and had its reactor changed. Then it was assigned to the Sixth Fleet in 1960. By this time, more advanced technologies were being developed and Nautilus functioned as a trainer sub after 1966.

Being able to travel the globe undetected meant that enemy military and commercial ships were exposed to submarine attack at any time and virtually any place on the Earth's oceans. Over time, the submarines were armed with ballistic missiles capped with nuclear warheads. A few years after the Nautilus, an alarmed Soviet Union developed its own nuclear submarine capabilities.

The development of nuclear submarines followed a similar arch with both nations -- first, submarines were developed that were powered by nuclear reactors but still used non-nuclear armaments. Then, submarines were both powered by reactors and armed with ballistic nuclear weapons.

The USSR didn't commission its first nuclear sub until 1958, and the submarine didn't cross the North Pole until 1962. The development of a nuclear submarine took the Soviets about five years' time from drawing board to commissioning. Early Soviet subs, such as the K-19 (known as the "Widowmaker"), were plagued by problems and resulted in several fatal accidents. The Soviet Union launched its first nuclear sub armed with ballistic nuclear missiles in 1960, the same year that feat was accomplished by the U.S. Throughout the Cold War, the Soviet Union continued produce (and still does produce) diesel-electric submarines armed with nuclear warheads.

Next, we'll learn how the U.S and the USSR put their nuclear subs to use during the Cold War.

Nuclear submarines weren't developed exclusively for use in the Cold War. Nuclear submarines came about as a result of technological advances; their use after creation, however, was a result of the Cold War.

At the time of the Manhattan Project (before the Cold War really began), there was some talk about the possibility of using nuclear power to propel submarines. The idea of arming submarines with nuclear missiles didn't come up until the 1960 launching of the George Washington. When nuclear energy was conceived of as a power source for submarines, that was a jaw-dropper in itself. But when navies gained the ability to launch a nuclear warhead from a nuclear-powered submarine, the world had touched on what was quite arguably the most powerful -- in terms of strength and mobility -- weapons system ever.

During the Cold War, the U.S. Navy developed two different types of nuclear-powered submarines. The first was a sub that could launch nuclear missiles at other nations, called a Fleet Ballistic Missile Submarine, also known as an SSBN or "boomer." The other was an Attack Submarine, signified as SSN, or "fast attack." SSBNs are the larger of the two, up to around 560 feet (170 m) in length, while SSNs are built with speed and stealth in mind, and are around 360 feet (109 m) in length.

Nuclear submarines served three primary roles during the Cold War: They performed strategic deterrence patrols, hunted other submarines and carried out special operations.

At least six nations now operate nuclear submarines: the U.S., Russia, India, France, China and the U.K. Several other nations, such as Brazil and Pakistan, are interested or actively attempting to develop (or purchase) nuclear-submarine capabilities. Nuclear submarines offer these nations a bit of prestige, not to mention enhanced offensive and defensive capabilities. As more nations seek to acquire this technology, navies must decide how to reconfigure their fleets (for more on this, read "Do we still need nuclear submarines?")

In the next section, we'll learn about the different parts and sections of a nuclear submarine.

Let's take a look at some of the basic parts of a nuclear submarine.

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Nitty-gritty Nuclear

Within the nuclear reactor, a neutron is used to split an atom of uranium, producing energy in the form of gamma radiation and heat. A coil filled with circulating water is superheated as it's routed past the reactor. This water is under extremely high pressure, which prevents it from boiling. Inside self-contained piping, the water is directed through a secondary source of water, where it's heated again. Here, the water is converted to steam and is piped toward the turbine that generates power for the submarine. The steam is condensed again in special cooling tubes, and the resulting water flows back into the steam generator. Inside the generator, it's reheated and the process repeats. This method requires no oxygen, so the submarine doesn't need to maintain or refresh a supply of air from above the surface.

Continue reading to find out why you should never bring a knife to a ballistic-missile fight.

As the means of propelling a submarine advanced, so, too, did the weaponry. During World War I, submarines were outfitted with deck guns, enabling them to approach commercial or military vessels while surfaced. While submarines had tactics for dealing with enemy submarines and utilized anti-ship missiles, World War II marked a submarine first when a British submarine destroyed a Nazi submarine using a torpedo. This was the first time that a submarine sank a ship; during World War I, the British sank 17 German subs. The British navy further modified its capabilities for attacking enemy vessels by employing fast subs armed with multiple torpedoes and early sonar.

In 1866, the first propeller-driven torpedo was invented [source: Brittanica]. Modern torpedoes are about 9 feet (2.7 m) long, carry 100 pounds (45 k) of explosives and can travel at 40 knots through the water toward their targets. Modern mines can contain as much as 500 pounds (226 k) of explosive material and are detonated when sensors detect certain magnetic, seismic or pressure-related input.

Once armed mainly with anti-sub missiles, as well as medium-range missiles for ships or distant subs, SSNs (fast attacks) are now outfitted with tactical Tomahawk cruise missiles that are able to strike faraway land targets with pinpoint accuracy. Tomahawks can be fired in any weather condition. Tomahawks can also be outfitted with a nuclear payload, or a 1,000-pound (453 k) warhead consisting of conventional explosives as well as multiple bomblets (a small bomb that's released midair to increase casualties). These cruise missiles are designed to fly at high speeds at low altitudes and are able to follow routes chosen for their evasive or stealth qualities.

SSBNs were initially armed with Polaris ballistic nuclear-armed missiles in the 1960s. The missiles took four years to develop and were designed to be ejected from the launch tube by gas pressure. This prevented the submarine from being damaged by the launch of the missile. Once it had navigated away from the submarine, the Polaris' rocket would engage. Though not especially accurate, the Polaris enabled the U.S. Navy to launch a nuclear missile from a concealed position beneath the surface from practically anywhere in the Earth's oceans.

There were three different versions of the Polaris missiles, and the Polaris was replaced by the Poseidon in 1972. The Poseidon missile was more accurate and had a greater range. In 1979, the Navy introduced to its submarines the first of the Trident class of missiles, the Trident I (C-4). Trident missiles could travel 4,000 nautical miles and could carry multiple warheads to be aimed at different targets. They were equipped with an aerospike that projected out of the nose cone (the front, top-end of the missile -- or the point) after launch to improve the aerodynamics of the missile.

The current weapons system carried by most American nuclear submarines is the Trident II (D-5). It's 44 feet (13 m) long, weighs 130,000 pounds (58,967 k) and can carry a larger payload than any of its predecessors. Each Trident II missile costs around $30 million to produce [source: US Navy].

In decades past, the Navy outfitted some of its submarines with nuclear-armed depth charges called Subrocs. Subrocs went operational in 1965 and were decommissioned in 1992. Subrocs were launched by rocket, traveled up to 35 miles (56 k) above the water's surface and then re-entered the water with a 5-kiloton nuclear warhead. It's remarkable that nuclear submarines were not only powered by nuclear energy and armed with nuclear weapons, but also equipped to wage a nuclear attack against rival submarines.

Next, we'll examine life aboard a nuclear submarine.

Life aboard a nuclear submarine isn't for everyone -- a sailor must undergo a battery of tests to determine his physical and mental abilities as well as his psychological and emotional well-being.

After passing early entry tests, a submariner receives formal training for about two months. He learns about the history of submarines, the different classes and types of submarines, engineering aspects, submarine weaponry, damage control measures (such as fire fighting) and team dynamics aboard the vessel.

­Depl­oyments on a submarine can vary in length, depending on the type of submarine. Overall assignments last three years. On a ballistic missile sub, two full crews rotate shifts to allow the vessel to remain at sea as often as possible. Each crew may serve for about 60 to 80 days before resurfacing and rotating out. This schedule is established for the entire three-year submarine assignment, allowing sailors and their families to plan their lives around the deployments.

Crews serving on fast attacks have more erratic mission assignments. A surveillance mission may last a few weeks -- or six months. Today, sailors can use e-mail (with some restrictions), but in times past, sailors weren't allowed to communicate with the outside world while aboard their sub.

A new submariner is called, without affection, a "puke" by the other sailors. Seasoned sailors know the boat inside and out and have already become qualified submariners, a process known as earning one's dolphins. This insignia is a badge of responsibility, brotherhood and honor. While a sailor who has already earned his dolphins may choose to relax or read in his off time, a puke must constantly study the ship's systems and pass a test on each one. Although a torpedo man or administrative officer won't need to know how to operate the nuclear reactor or the navigational systems, both will be trained to understand the systems, their safeguards and emergency procedures. Once a puke has been tested on every part of the ship by a qualified submariner, he earns his dolphins in a special ceremony and is accepted as a member of the nuclear family.

But drilling doesn't end once a sailor gets his dolphins. The crew constantly trains to handle various casualties, such as fire or flood. In addition to keeping the crew ready for any emergency, these drills also help shipmates pass the time. A submarine "day" lasts 18 hours and is split into three six-hour shifts. So a submariner may work for six hours and train, maintain equipment or sleep for 12 hours.

Bunks are generally stacked three high. Space is at a premium in a submarine, and little of it is afforded to each sailor. Some submariners may have to hot-bunk -- get into a bunk that has just been vacated by a shipmate starting his shift. A curtain provides privacy, and a small locker or drop-down shelf is all each submariner has for storage.

In addition to many safeguards in place within and around the nuclear warheads and the reactor, submariners are monitored for radiation exposure or sickness. Nuclear safety is taken very seriously -- public relations and recruitment would be considerably more difficult if submariners were ending their two-month deployment at sea without hair, teeth or white blood cells.

There are currently no women on any United States nuclear submarine. The reason for this is twofold: There's no privacy whatsoever, and reconfiguring submarines to facilitate the cohabitation of both sexes would cost a good deal of money and take space away from other submarine functions.

Continue reading to learn about other uses of nuclear seacraft.

We've learned about the military applications of a nuclear submarine. What are some of its other uses?

The incredible range of a nuclear submarine makes it ideal for exploration. A nuclear submarine first reached the North Pole in 1958. It was a feat made possible by simply navigating the submarine beneath the ice caps found at either pole, and then surfacing by breaking through the ice. Prior to this, exploration of the polar area was extremely difficult. Personnel and materials had to be carried overland through a harsh and bitterly cold environment. Research stations had to be built, maintained and resupplied.

Even today, harsh weather conditions limit overland access to the area at certain times of the year (in addition to subfreezing temperatures, "winter" consists of about six months of uninterrupted darkness). Now, a research team can travel in relative comfort and emerge directly in the middle of an ice cap. The nuclear submarine itself is a self-contained survival unit, and so can directly support a scientific team on a short-term mission.

The unlimited range of a nuclear submarine enabled researchers to take samples of and study different parts of the open seas at the Earth's poles, instead of being confined to conducting studies close to shore. Using sonar and other means, oceanographers have been able to survey and map the ocean floor at both the North and South Pole.

Though the Navy's own research is almost exclusively tied to military functio­ns, it has paved the way for future researchers to access these remote areas to study the aquatic life, search for medicinal elements and analyze the air and shape of the icecaps for signs of environmental damage.

In 1969, the Navy developed the NR-1, a 140-foot-long research submersible that was powered by a refrigerator-sized nuclear reactor. Designed to reclaim sunken enemy subs from great depths, the NR-1 enabled small teams of about seven researchers to conduct studies and take samples as far down as half a mile below the surface. Other than to replenish supplies, the NR-1 can remain in a state of controlled submergence at such depths indefinitely.

In one survey of Scandinavian waters, the NR-1 located the wrecks of 26 ships in half a day. It also was used to locate wreckage from jet fighters and even pinpointed the remains of Challenger space shuttle.

Modern nuclear vessels are capable of reaching great depths, enabling scientists to study the deep-sea creatures and thermal vents found along the ocean's floor.

Continue reading for lots more information about nuclear submarines.