Named for the 24, Trident II Submarine-launched ballistic missiles (SLBMs) they carry, the Ohio-class submarines were designed specifically for extended war-deterrence patrols. Each of these submarines are provided with two complete crews, called the Blue crew and the Gold crew, with each crew serving typically on 70 to 90 day deterrent patrols.
Ballistic missile submarines have been of great strategic importance to the United States and other nuclear powers since the start of the Cold War, as they can hide from reconnaissance satellites and fire their nuclear weapons with virtual impunity. This makes them immune to a first strike directed against nuclear forces, allowing each side to maintain the capability to launch a devastating retaliatory strike, even if all land-based missiles have been destroyed.
Trident II Missiles
These missiles launch from underwater in a vertical missile tube inside the submarine. They rapidly ascend to the surface inside a gas bubble. Flying out of the ocean, internal gyros let the missile know when it’s beginning to fall back towards the water. This triggers the rockets to fire sending the Intercontinental Ballistic Missile thousands of miles towards its target.
They typically deliver multiple independently targetable reentry vehicles (MIRVs), each of which carries a nuclear warhead and allows a single launched missile to strike several targets.
How Submarines Work
Submarines are designed for use at great depths. Their rigid, double-walled hulls allow the crew to live and work normally underwater for as long as air and power supplies last. Submarines are steered by turning a rudder left and right. A propeller moves the sub through the water, pushing water backward so that the submarine moves forward.
The crucial problem for a submarine is that it must either sink or float on command. Most things either sink or float, but can’t do both. Why? When an object is placed into water, it either sinks or floats according to its density. Objects denser than water (like metal) sink, while objects less dense than water (like air-filled balloons) float. What about a submarine?
Submarines are a mixture of metal (the hull), air, and water (the “ballast”). The secret of a submarine’s ability to either sink or float lies in a special property of air. Unlike water or metal, air can be squashed into a tiny space. While the submarine is sinking, its air is compressed. Water fills the compartments called the ballast tanks. The combination of water and metal, with just a little bit of air in the centre for the crew to breathe, is more dense than the surrounding ocean water, and so the submarine sinks.
Once the submarine is underwater, air is pumped into the ballast tanks. The new combination of metal, water, and air is just as dense as the surrounding water, so the submarine hovers, neither sinking nor rising. This is called “neutral buoyancy”, and allows the sub to maneuver underwater.
When it’s time to rise, even more air is pushed into the ballast tanks. This pushes water out, resulting in a mixture of air, metal, and water that is now less dense than the water surrounding the sub. Under these conditions, the sub rises to the surface.
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. 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.
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 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, showering, and other personal hygiene).
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.
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 a nuclear reactor that uses 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.
Despite all the cosmic energy that the word “nuclear” invokes, power plants that depend on atomic energy don’t operate that differently from a typical coal-burning power plant. Both heat water into pressurized steam, which drives a turbine generator. The key difference between the two plants is the method of heating the water.
While older plants burn fossil fuels, nuclear plants depend on the heat that occurs during nuclear fission, when one atom splits into two and releases energy. Nuclear fission happens naturally every day. Uranium, for example, constantly undergoes spontaneous fission at a very slow rate. This is why the element emits radiation, and why it’s a natural choice for the induced fission that nuclear power plants require.
Uranium is a common element on Earth and has existed since the planet formed. While there are several varieties of uranium, uranium-235 (U-235) is the one most important to the production of both nuclear power and nuclear warheads.
U-235 decays naturally by alpha radiation: It throws off an alpha particle, or two neutrons and two protons bound together. It’s also one of the few elements that can undergo induced fission. Fire a free neutron into a U-235 nucleus and the nucleus will absorb the neutron, become unstable and split immediately.
As soon as the nucleus captures the neutron, it splits into two lighter atoms and throws off two or three new neutrons (the number of ejected neutrons depends on how the U-235 atom splits). The process of capturing the neutron and splitting happens very quickly.
The decay of a single U-235 atom releases approximately 200 MeV (million electron volts). That may not seem like much, but there are lots of uranium atoms in a pound (0.45 kilograms) of uranium. So many, in fact, that a pound of highly enriched uranium as used to power a nuclear submarine is equal to about a million gallons of gasoline.
The splitting of an atom releases an incredible amount of heat and gamma radiation, or radiation made of high-energy photons. The two atoms that result from the fission later release beta radiation (superfast electrons) and gamma radiation of their own, too.
In order to turn nuclear fission into electrical energy, nuclear power plant operators have to control the energy given off by the enriched uranium and allow it to heat water into steam.
Enriched uranium typically is formed into inch-long (2.5-centimeter-long) pellets, each with approximately the same diameter as a dime. Next, the pellets are arranged into long rods, and the rods are collected together into bundles. The bundles are submerged in water inside a pressure vessel. The water acts as a coolant. Left to its own devices, the uranium would eventually overheat and melt.
To prevent overheating, control rods made of a material that absorbs neutrons are inserted into the uranium bundle using a mechanism that can raise or lower them. Raising and lowering the control rods allow operators to control the rate of the nuclear reaction. When an operator wants the uranium core to produce more heat, the control rods are lifted out of the uranium bundle (thus absorbing fewer neutrons). To reduce heat, they are lowered into the uranium bundle. The rods can also be lowered completely into the uranium bundle to shut the reactor down in the event of an accident or to change the fuel.
The uranium bundle acts as an extremely high-energy source of heat. It heats the water and turns it to steam. The steam drives a turbine, which spins a generator to produce power. Humans have been harnessing the expansion of water into steam for hundreds of years.
In some nuclear power plants, the steam from the reactor goes through a secondary, intermediate heat exchanger to convert another loop of water to steam, which drives the turbine. The advantage to this design is that the radioactive water/steam never contacts the turbine. Also, in some reactors, the coolant fluid in contact with the reactor core is gas (carbon dioxide) or liquid metal (sodium, potassium); these types of reactors allow the core to be operated at higher temperatures.
Due to their steel hulls, 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.
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.
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.
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.
All About Water
- Water covers 70.9% of the Earth’s surface.
- Only 3% of the Earth’s water can be used as drinking water. The other 97% resides in the oceans, which contains a harmful level of salt (3.5%) for people, agriculture, and livestock.
- Each day the sun evaporates roughly a trillion tons of water which returns as precipitation.
- Water is the only substance on Earth that can naturally be found as a gas, solid, or liquid. It boils at 212 degrees Fahrenheit or 100 degrees Celsius. It freezes at 32 degrees Fahrenheit or 0 degrees Celsius.
- The water molecule is known as Dihydrogen monoxide or H2O since it contains one Oxygen atom and two Hydrogen atoms.
- The human body contains from 55% to 78% water, depending on body size.
- Approximately 2 liters (6 to 7 glasses) of water daily is the minimum to maintain proper hydration for people.