Submarine Engineering

Summary

Submarines are naval vessels capable of operating beneath the surface of the water. The early models were powered by simple diesel engines, but most modern submarines are nuclear-powered. The world's navies operate most submarines, which are used as military vessels during wars. The submarine's ability to submerge beneath the waves allows it to hide from adversaries and avoid detection while carrying out its mission. Submarines are also used in civilian scientific capacities to study the deep portions of the ocean inaccessible by traditional diving methods.

Definition and Basic Principles

Submarine engineering is the field of designing, constructing, and improving submarines to work in their unique environment. Submarines are the only moving human-made objects designed to operate underwater, a hostile environment with many hazards and potential dangers to both the vessel and crew. In addition, most submarines are weapons of war and must deal with the threat of combat in addition to the perils of the sea. Early submarines were more accurately submersibles, craft that could submerge beneath the surface but that spent most of their time on the surface. Early submarines possessed only limited electric battery power to drive the engines while submerged. They had to return to the surface after a relatively short period to recharge their batteries. Modern submarines, especially those with nuclear power, are true submarines, spending most of their time submerged and little time on the surface.

As tools of war, the weapons found on submarines have also changed over time to deal with different threats. Early submarines were armed with simple explosive charges on the end of a pole, but the invention of the torpedo in the late nineteenth century gave submarines a long-distance weapon that allowed them to take full advantage of their ability to hide underwater, sneak up on an enemy vessel, and destroy it. By the late twentieth century, submarines came equipped with modern offensive and defensive systems.

Submarines are also used in peaceful pursuits. Small research submarines are ideally suited to explore the depths of the ocean because they can go much deeper than divers equipped with portable sources of oxygen. Because of the intense water pressure found in deep waters, these research submarines must be built very strong. Despite the dangers of operating at depth, submarines have visited even the deepest portions of the ocean, thousands of feet beneath the surface. By late 2019, Victor Vescovo, a businessperson and adventurer, had privately funded and commissioned the construction of an advanced submersible that allowed him to be declared the first person to dive to the deepest points of Earth's named oceans. Private submersibles also gained media attention in 2023 when the United States (US) company OceanGate, focused on providing submersibles for tourism and research, lost a submersible carrying passengers to visit the wreck of the Titanic. 

Background and History

Although several inventors tried to construct submarines before the Industrial Revolution, none succeeded because they lacked an effective power source. These early submersibles, such as David Bushnell's Turtle, built in 1776, failed because they had to rely on human power. Later, when steam power became available, inventors, such as Robert Fulton, designed powered submarines. Still, the steam engines could not work underwater because they needed a source of oxygen for the fires in their boilers.

In 1897, the American inventor John Holland solved most of these problems. His submarines, albeit small, featured two power sources. The submarine had an electric motor that ran on large batteries for operating underwater and a diesel engine for cruising on the surface. The diesel engine also ran a dynamo to recharge the batteries so the submarine could spend more time underwater. The US Navy, along with agencies from several other countries, purchased Holland's submarine design. By the twentieth century, submarines had matured into advanced weapons of war, and in both World War I and World War II, submarines sank thousands of enemy ships on both sides of the conflict.

The biggest weakness of the submarine was its periodic need to resurface to recharge its batteries. That problem was solved in 1954 when the US Navy commissioned the USS Nautilus, the first nuclear-powered vessel in the world. With an unlimited amount of power that did not need an oxygen supply, nuclear-powered submarines could stay submerged indefinitely, and because they did not need to take on diesel fuel, they could also operate at full power indefinitely, allowing them to range across the ocean with little fear of discovery. In the twenty-first century, many private companies offer submersibles to be used in tourism and research. However, ethical and safety concerns abound regarding private use.

How It Works

Diving and Maneuvering. Submarines, with their ability to operate beneath the surface, require special equipment to disappear below the surface (and come back up) and to maneuver while in the water. On the surface, the submarine operates like a traditional ship, relying on buoyancy to remain afloat and a rudder to maneuver. To submerge, however, submarines must lose their buoyancy, which is accomplished using ballast tanks. When the submarine is on the surface, the ballast tanks are filled with air. When the air is compressed into tanks, and the ballast tanks fill with water, the submarine becomes heavy enough to submerge. Once submerged, the submarine maneuvers using diving planes, small “wings” attached to the hull that direct the water flow past the submarine, to maneuver the submarine up or down. To surface, the submarine blows the stored air back into the ballast tanks, and the submarine rises. In the late 2010s, scientists invested more focus on experimenting with electromagnetic propulsion systems. It was predicted that this kind of system would take up less space in submarines and make them quieter. By 2024, the USS Columbia, the first of the Columbia-class ballistic missile submarine, as the new electric fleet is named, was under construction at a Rhode Island shipyard. Although its construction was slightly delayed, the USS Columbia was announced to go into naval service by 2031.

Propulsion. Early submarines required two things that limited their range and ability to stay underwater: air and battery power. Large battery arrays allowed submarines to remain submerged only for a limited time. Submarines had to use their diesel engines to recharge the batteries, but the diesel engines needed air, so the recharging had to occur on the surface. The advent of nuclear power in the 1950s, however, removed the major limitations on propulsion. Nuclear power plants did not need air to operate, and the nuclear submarine's steam turbine did not need batteries. Because of these features, some modern submarines are employed on missions during which they may not surface for six months or more. By the 1990s, new air-independent propulsion systems permitted the operation of diesel engines underwater without the expense of a nuclear power plant.

Sensors. Early submarines relied on human sight to sense obstacles and targets around them. This led to the creation of the conning tower, a structure built atop the submarine hull that allowed a lookout to view the area around the submarine while the bulk of the vessel remained just below the surface of the water. Once submerged, early submarines were blind and needed other means to find their way. After World War I, submarines used hydrophones, sensitive microphones mounted on the submarine hull, to listen for other ships and submarines around them. By the 1950s, sonar allowed submarines to actively detect other vessels.

Navigation. When early submarines submerged, they lost their ability to navigate because they lacked external reference points, such as the stars, by which to navigate. Submarines had to navigate into the general area of a target, and then submerge to conduct their attack. When nuclear submarines began to spend more time submerged than surfaced, crews needed a more accurate means of establishing their location, especially after submarines were armed with nuclear missiles that required precise targeting. The solution was inertial navigation, whereby the submarine crew took extremely precise measurements from motion sensors mounted throughout the submarine and used the data relative to the amount of time and direction the submarine had traveled to calculate their location.

Stealth. Submarines can hide beneath the ocean, but that does not mean they are not detectable. Sonar allows aircraft, surface ships, and other submarines to detect the presence of submarines because of the noise they generate. To counter this, submarines strive to be extremely quiet, and all efforts are made to eliminate or suppress noise. Submarine propellers move very slowly to limit cavitation, the creation of air bubbles as the propeller blade moves through the water. A submarine's machinery is placed on racks fitted with rubber cushions so that the machinery vibration is not transmitted into the hull and then into the water. Many submarines are coated on the outside with anechoic tiles, a material that absorbs sonar waves instead of bouncing them back.

Shape. Early submarines were shaped like surface craft. They were long and narrow and had a pointed bow to pierce the waves. Although this shape worked well on the surface, it was not suitable for underwater speed, as the hull shape created drag that was not hydrodynamic. When nuclear power permitted submarines to spend virtually all of their time submerged, hull forms began to reflect the change. Early nuclear submarines had hulls with a tubular cigar shape, but by the 1960s, US nuclear submarines had adopted a teardrop shape that emulated the shape of whales, with a bulbous bow and a stern that tapered to a point. This was the most hydrodynamic shape, and all subsequent submarines have copied it.

Armament. The invention of the torpedo in the late nineteenth century made the submarine an effective ship-destroying weapon, but submarines also had other weapon systems. Most submarines carried a deck gun in the 4- to 6-inch caliber range to deal with unarmed targets. When aircraft became a viable weapon, submarines began to carry light antiaircraft guns in the 20- to 40-millimeter caliber range for self-defense. After nuclear power permitted submarines to stay underwater most of the time, these deck-mounted weapons became unnecessary. Instead, submarines added missiles to their armament. Submarines still used increasingly advanced torpedoes, but by the late twentieth century, they could fire either ballistic missiles armed with nuclear weapons or long-range cruise and anti-ship missiles.

Applications and Products

Military Use of Submarines. The technological breakthroughs that led to the modern submarine make it the most lethal naval weapons system available to any nation that can afford it. As military craft, submarines fulfill three functions: defending shores, attacking enemy ships and submarines in the open ocean, and launching ballistic missiles.

Small diesel-electric submarines, usually equipped with air-independent propulsion systems, are used for coastal defense and short-range local operations, where their limited diving depth and relatively short operational range is not a limitation. As diesel-electric submarines are less expensive than nuclear-powered submarines, they are most common in the navies of smaller countries with less money to spend on defense.

Larger attack submarines, usually nuclear powered, are used to patrol the open ocean during wartime, searching for and sinking enemy surface ships and submarines. Submarines can sneak up close to possible targets and destroy them with either modern torpedoes or long-range cruise missiles. Because of their stealth features, attack submarines are often used for intelligence-gathering missions against possible enemies.

The last military use of submarines is as missile carriers. These submarines, known as ballistic missile submarines, carry several long-range ballistic missiles armed with nuclear warheads and act as a reliably safe deterrent to enemy nuclear attack. Land-based nuclear forces are vulnerable because they are visible and therefore vulnerable to enemy attack, but submarine-based missiles hiding and moving beneath the ocean are virtually untraceable. The first ballistic missile submarine, the USS George Washington, was commissioned into the US Navy in 1959. Several countries other than the US also operate ballistic missile submarines.

Civilian Use of Submarines. Not all submarine engineering is for military purposes. Technological advances allowed for expanded civilian use of submarines. Several oceanographic and scientific institutes operate deep diving research submarines, known as bathyscaphes or deep submergence research vessels (DSRVs), to explore the ocean's depths. They are also used to inspect and maintain underwater facilities, oil exploration, and salvaging. These scientific submarines are very different from military submarines. Although military submarines must be large to range across the oceans, research submarines are typically small, have a limited range, and must be conveyed to their research area by a supporting surface ship. Although military submarines have a relatively limited maximum diving depth, generally about 1,000 feet, research submarines are constructed with thick walls to survive depths significantly deeper. In 1960, a US-Swiss research submarine, the Trieste, reached the bottom of Challenge Deep, the deepest point in the world, at a depth of more than 36,000 feet.

The other primary civilian use of submarines is for entertainment and tourism. A number of resorts, especially in the Caribbean, use small submarines to take fee-paying tourists on a short and shallow ride into the ocean. The submarines are popular because they allow the rider to view the ocean and its wildlife in a comfortable, safe environment. The submarine also eliminates the need for bulky scuba gear and being trained in its use. Instead, tourists can simply climb aboard and see much of what a scuba diver would without the expense and inconvenience. However, the recreational use of submarines and submersibles has also received negative publicity. Adventurers, sometimes blinded by wealth and ambition, have created private submersibles that travel to depths much deeper than those at resorts and create dangerous situations for themselves and their passengers. The loss of the OceanGate Titan in 2023, which imploded due to design flaws while carrying passengers to the wreck of the Titanic, is one example of the dangers of modern, private submersibles. 

Careers and Course Work

Submarine engineering requires very specialized and advanced training, usually a Doctorate, in addition to several years of experience in the form of training or apprenticeship. In addition to basic shipbuilding, engineers in the submarine field require advanced training in the particular attributes and challenges of constructing ships designed to go underwater. Materials engineering, especially involving high-tensile steels, is a prime example of a specialized skill required to construct a submarine. Engineering of nuclear power plants is a process separate from ship construction and requires an equal amount of specialized training in the design, use, and handling of nuclear fuels. Because of the myriad subsystems in every submarine, engineering related to submarine construction includes fields ranging from electrical/electronic engineering to environmental engineering and waste management. Coursework required for such a level of engineering involves advanced engineering in a range of subdisciplines, including chemistry, metallurgy, and computer-aided design.

Social Context and Future Prospects

As a military weapon, submarines, especially nuclear ones, are stealthy, capable, and flexible in the missions they can accomplish. They can dominate large areas of ocean and their ability to carry a variety of weapons systems makes them useful to navies that have them and attractive to navies that want them. As the backbone of a nation's nuclear deterrent force, missile-firing submarines, although expensive, are less vulnerable than land-based systems, guaranteeing their presence in the world's major navies for the foreseeable future.

Civilian submarines are also an area of growing interest. Although scientific submarines have mapped significant portions of the oceans, most of the ocean floor remains unexplored. By the end of his mission to reach the deepest points of each of the named oceans, called the Five Deeps Expedition, in 2019, Vescovo and his team had donated large amounts of unmeasured seafloor data to ongoing international efforts to map the ocean floor and had contributed information regarding temperature, salinity, and deep ocean biology. As natural resources on the land become scarcer, humanity will rely more and more on the ocean to fill the need for materials, and the exploration of the ocean has taken on even more significance. Civilian submarines also fill the need to educate the public about environmental protection. By providing a view of the ocean and demonstrating its importance to human survival, civilian submarines promote environmentalism and the preservation of natural resources. As the twenty-first century progressed, civilian submarines grew in number and popularity. The number of submarines built for private ownership also increased. These were smaller, with the ability to carry only a few passengers at a time, and were intended for recreational use.

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