This chapter was published on “Inuitech – Intuitech Technologies for Sustainability” on August 8, 2011
As of November 2010, about 140 ships are powered by more than 180 small nuclear reactors and more than 12,000 reactor years of marine operation has been accumulated. Most of these ships represent submarines, but they range from icebreakers to aircraft carriers. In the last fifty-five years since the first nuclear propelled voyage in 1955, five of the world’s navies have well over a combined one hundred million miles of nuclear powered ocean travel using more than 700 marine nuclear reactors.
1. NUCLEAR MARINE PROPULSION – HIGHLIGHTS
Here are some characteristics of nuclear marine propulsion:
- Naval nuclear reactors with a high enrichment level of 93 percent, capable of reaching 97.3 percent in Uranium235, are designed for a refueling after 10 or more years over their 20-30 years lifetime. Whereas land based nuclear reactors, use fuel enriched to 3-5 percent in Uranium235 and need to be refueled every one to one and half years. The focus of new core designs is to last 50 years in aircraft carriers and 30-40 years in submarines. This is the design goal of the Virginia class of submarines.
- Naval nuclear reactors use high burnup fuels such as uranium-zirconium, uranium-aluminum, and metal ceramic fuels in contrast to land-based nuclear reactors, which use uranium oxide (UO2). These factors provide the naval vessels theoretical infinite range and mission time. For these two considerations it is recognized that a nuclear reactor is the ideal engine for naval propulsion.
- The safety record of the US nuclear navy is excellent and attributed to a high level of standardization in naval power plants, their maintenance, and the high quality of the naval training program. While early Soviet endeavors resulted in a number of serious accidents, five of those accidents involved the reactors which where irreparably damaged and resulted in radiation leaks. However, by Russia’s third generation of marine Pressurized Water Reactor (PWR) (in the late 1970s) safety and reliability had become a high priority; and
- The Russian, British, and US navies rely on steam turbine propulsion while the French and Chinese in their submarines use the turbine to generate electricity for propulsion.
At the end of the Cold War, in 1989, there were over 400 nuclear-powered submarines operational or being built. At least 300 of these submarines have now been scrapped and some on order cancelled due to weapons reduction programs. Russia and USA had over one hundred each in service with the UK and France less than twenty each and China.
2. NUCLEAR MARINE PROPULSION – DEFINITION:
Nuclear marine propulsion is commonly defined as a ship or submarine engine driven by steam generated by nuclear energy in a reactor, rather than the combustion of fuel in a boiler. A nuclear-powered ship is constructed with the nuclear power plant inside a section of the ship in the reactor compartment. The components of the nuclear power plant include a high-strength steel reactor vessel, heat exchanger(s) and steam generator, and associated piping, pumps, and valves. Each reactor plant contains over 100 tons of lead shielding. Part of this shielding is made radioactive by contact with radioactive material or by neutron activation of impurities in the lead. The following are considered nuclear marine vessels:
2.1 Nuclear Submarines:
A nuclear submarine is a submarine powered by a nuclear reactor. Submarines are extremely popular with world navies and this category of vessel will include the following four general types:
- Ballistic Missile Nuclear-Powered Submarines (SSBN) – SSBN, the most powerful warships afloat are operated by only a few of the world’s nuclear powers: China, France, Russia, the United Kingdom, and the United States;
- Nuclear-Powered Attack Submarines (SSNs) – SSNs are the most capable general-purpose submarines, but only a few blue-water nations (China, France, Russia, the United Kingdom, and the United States) can currently afford to build and operate nuclear submarines. However, Brazil and India have programs in place to develop an indigenous nuclear submarine construction capability;
- General Purpose Diesel-Electric Submarine (SS) – Diesel-electric submarines are the most common submarines and are operated by a large number of the world’s navies; AND
- Small Special Purpose Midget Submarines and Swimmer Delivery Vehicles – This would include small midget submarines such as the COSMOS type as well as dry and wet swimmer delivery vehicles.
2.2 Nuclear Aircraft Carriers:
A nuclear aircraft carrier is a warship powered by a nuclear reactor. An aircraft carrier is a warship designed with a primary mission of deploying and recovering aircraft, acting as a seagoing airbase. Aircraft carriers thus allow a naval force to project air power worldwide without having to depend on local bases for staging aircraft operations. They have evolved from wooden vessels, used to deploy balloons, into nuclear powered warships that carry dozens of fixed and rotary wing aircraft.
2.3 Nuclear Cruisers:
A nuclear cruiser is a ship powered by a nuclear reactor. A cruiser is the largest type of surface combatant currently in-service or planned for service in world navies. A cruiser generally displaces over 10,000 tons and is fully capable of a wide-range of independent warfare operations in a multi-threat environment.
2.4 Nuclear Destroyers:
A nuclear destroyer is a ship powered by a nuclear reactor. A destroyer is smaller and less capable than a cruiser, but is also capable of operating independently in a high-threat environment. Destroyers have steadily grown in size (now 5,000 to 10,000 tons), expense (nearly US$700 million apiece) and capability. Generally, a destroyer is considered to be a ship that has all of the sensors (including sophisticated phased-array radar), combat systems, and weapons needed to operate in a high-threat environment. A number of world navies are currently building ships that, while called frigates, more accurately represent destroyers in size and capability. Examples include the Spanish F-100, the German F-124, and the Dutch De Zeven Provincien classes (all are highly capable ships displacing over 5,000 tons and carrying phased-array radars).
Here is a graphical representation (Figure: 9-1) of a PWR which is commonly used for nuclear marine propulsions:
According to the World Nuclear Association, naval reactors, with the exception of the ill-fated Russian Alfa class, have been pressurized water types, which differ from commercial reactors producing electricity:
- These reactors deliver a lot of power from a very small volume and therefore run on highly-enriched uranium (>20 percent U-235, originally c 97 percent but apparently now 93 percent in latest US submarines, c 20-25 percent in some western vessels, 20 percent in the first and second generation Russian reactors 1957-81, then 45 percent in 3rd generation Russian units, 40 percent in India’s Arihant);
- The fuel is not UO2 but a uranium-zirconium or uranium-aluminum alloy (c15 percent U with 93 percent enrichment, or more U with less – eg 20 percent – U-235) or a metal-ceramic (Kursk: U-Al zoned 20-45 percent enriched, clad in zircaloy, with c 200kg U-235 in each 200 MW core);
- The reactors have long core lives so that refueling is needed only after 10 or more years, and new cores are designed to last 50 years in carriers and 30-40 years (over 1.5 million kilometres) in most submarines;
- The design enables a compact pressure vessel while maintaining safety. The Sevmorput pressure vessel for a relatively large marine reactor is 4.6 m high and 1.8 m diameter, enclosing a core 1 m high and 1.2 m diameter;
- The thermal efficiency is less than in civil nuclear power plants due to the need for flexible power output and space constraints for the steam system; and
- There is no soluble boron used in naval reactors (at least US ones).
The submarines during World War II used diesel engines that could be run at the surface charging a large bank of electric batteries which could later be used while the submarine was submerged until discharged. At this point the submarine had to surface to recharge its batteries and became vulnerable to detection by aircraft and surface vessels.
The concept of the nuclear submarine was capitalized at the beginning of the 1950s by both the US and the Soviet Union – when the Cold War between those countries was at pinnacle. Both countries were trying technologies to build nuclear powered submarines to overcome the drawbacks of conventional ones. Both countries knew the strategic value of using nuclear reactors to power naval vessels.
Scientists in both the US and the Soviet Union were intensely engaged in exploring the possibilities of using nuclear engines to power submarines, which could allow longer intervals of time for refueling the submarines. They were convinced that a nuclear engine could enable submarines to travel long distances undetected at high speed underwater avoiding the surface wave resistance, without refueling. Unlike diesel engine driven submarines, the nuclear engine would not require oxygen to produce its energy.
3. US NUCLEAR MARINE PROPULSION:
The US Navy contracted out the construction, testing, and operation of a prototype pressurized water reactor plant to the Westinghouse Electric Corporation and this first reactor plant was called the Submarine Thermal Reactor (STR). The STR was brought to power for the first time on March 30, 1953 and the age of naval propulsion was born.
The STR achieved a 96 hour sustained full power run simulating a crossing of the Atlantic Ocean in 1953. The second SIW core sustained, in 1955, a 66 day continuous full power run simulating a high speed run twice around the globe. The STR was redesigned as the first generation submarine reactor SIW which was used as the prototype of the USS Nautilus – SSN571 (Figure 9-2) reactor and was followed in the middle to late 1950s by the aircraft carrier AIW – the prototype of the aircraft carrier USS Enterprise plant.
Under the leadership of Admiral Hyman G. Rickover, the first nuclear-powered submarine, USS Nautilus – CCN-571 (Figure: 9-2) which utilized the STR prototype, started its first operation on December 30, 1954 and it reached full power operation on January 13, 1955. This marked the transition of submarines from slow underwater vessels to warships capable of sustaining 20-25 knots submerged for weeks on end. Much of the early development work on naval reactors was done at the Naval Reactor Facility on the campus of the Idaho National Laboratory in the United States of America.
Nautilus set speed, distance and submergence records for submarine operation that were not possible with conventional submarines. It was the first ship to reach the North Pole. It was decommissioned in 1980 after 25 years of service, 2,500 dives, and a travelled distance of 513,000 miles. It is preserved at a museum at Croton, Connecticut.
The nuclear reactor for the Nautilus was a high water moderated, with highly enriched Uranium235 core, with zirconium clad fuel plates. The high fuel enrichment gives the reactor a compact size and a high reactivity reserve to override the xenon poison dead time. The Nautilus beat numerous records establishing nuclear propulsion as the ideal driving force for the global submarine fleet. Among its feats was the first underwater crossing of the Arctic ice cap. It travelled 1,400 miles at an average speed of 20 knots. On a first core without refueling, it travelled 62,000 miles.
The second nuclear submarine of the US Navy, the USS Seawolf – SSN-575 (Figure: 9-3), had a Sodium-Cooled Power Reactor (S2G), which operated for early two years from 1957 to 1958. The intermediate-spectrum reactor raised its incoming coolant temperature over ten times as much as the Nautilus‘ water cooled plant, providing superheated steam, and it offered an outlet temperature of 454°C (849 Degree Fahrenheit), compared with the Nautilus’ 305°C. It was highly efficient, but offsetting this, the plant had serious operational disadvantages. Large electric heaters were required to keep the plant warm when the reactor was down to avoid the sodium freezing. The biggest problem was that the sodium became highly radioactive with a half-life of 15 hours so that the whole reactor system had to be more heavily shielded than a Water-Cooled Reactor, and the reactor compartment could not be entered for many days after shutdown. The reactor was replaced with a PWR type (S2Wa) similar to Nautilus.
USS Enterprise, CVN-65 (Figure: 9-4) is the world’s first nuclear powered aircraft carrier. The only ship of her class Enterprise is the second-oldest vessel in commission in the US Navy after the wooden-hulled, three-masted frigate USS Constitution.
The largest experience in operating nuclear power since the 1950s has been in nuclear marine propulsion, particularly aircraft carriers and submarines. The nuclear powered vessels comprise about 40 percent of the US Navy’s combatant fleet, including the entire sea based strategic nuclear deterrent. All the US Navy’s operational submarines and over half of its aircraft carriers are nuclear powered.
By 1962 the US Navy had 26 nuclear submarines operational and 30 under construction. Nuclear power had revolutionized the Navy. The technology was shared with the United Kingdom, while French, Russian, Indian, and Chinese developments proceeded separately.
As of 2001 about 235 naval reactors had been built with a unit cost of about $100 million for a submarine and $200 million for an aircraft carrier. By 2002, the US Navy operated 53 attack submarines (SSN) and 18 ballistic missile submarines (SSBN). These vessels used (by 1999) about 129 nuclear reactors exceeding the number of commercial power plants at 108.
The US has the main navy with nuclear-powered aircraft carriers, while both – the US and Russia – have had nuclear-powered cruisers (US: 9, Russia 4). The US had built 219 nuclear-powered vessels to mid 2010 and then had five submarines and an aircraft carrier under construction. All US aircraft carriers and submarines are nuclear-powered.
The US Navy, as of 2008, operated 99 vessels powered by nuclear reactors including 10 nuclear powered aircraft carriers and 71 submarines. The US Navy has accumulated over 6200 reactor-years of accident-free experience over the course of 230 million kilometres, and operated 82 nuclear-powered ships (11 aircraft carriers, 71 submarines – 18 SSBN/SSGN, 53 SSN) with 103 reactors as of March 2010.
4. RUSSIAN NUCLEAR MARINE PROPULSION:
The Soviet Union started its nuclear submarine program in the 1950s, too. Its research work was conducted at Institute of Physics and Power Engineering at Obninsk. They began testing their models in 1956 and finally after many obstacles like radiation leaks and steam generation problems their first nuclear powered submarine entered service in Soviet Navy on 1958.
Russia built 248 nuclear submarines and five naval surface vessels (plus nine icebreakers) powered by 468 reactors between 1950 and 2003, and was then operating about 60 nuclear naval vessels. In 2007, Russia had about 40 retired subs from its Pacific fleet alone waiting to be scrapped. In November 2008, it was reported that Russia intended to scrap all decommissioned nuclear submarines by 2012, the total being more than 200 of the 250 built to date. Most Northern Fleet submarines had been dismantled at Severodvinsk and most remaining to be scrapped were with the Pacific Fleet.
The largest submarines (Figure: 9-5) are the 26,500 tonne Russian Typhoon-Class, powered by twin 190 MWt PWR reactors, though the 24,000 t Oscar-II class (eg Kursk) with the same power plant superseded these.
The Russian Navy has logged over 6000 nautical reactor-years. It appears to have eight strategic submarines (SSBN/SSGN) in operation and 13 nuclear-powered attack submarines (SSN) plus some diesel subs. Russia has announced that it will build eight new nuclear SSBN submarines in its plan to 2015. Its only nuclear-powered carrier project was cancelled in 1992. It has one nuclear powered cruiser in operation and three others are being overhauled.
The Russian ALFA-Class submarines (Figure:9-6) had a single liquid metal cooled reactor (LMR) of 155 MWt and using very highly enriched uranium – 90 percent enriched U-Be fuel. These were very fast, but had operational problems in ensuring that the lead-bismuth coolant did not freeze when the reactor was shut down. The design was unsuccessful and used in only eight trouble-plagued vessels.
The ALFA-Class submarine was the fasted submarine in service in any navy. It was a deep diving titanium submarine, which had a submerged speed estimated to be over 40 knots. The titanium hull provided strength for deep diving. It also offered a reduced weight advantage leading to higher power to weight ratios resulting in higher acceleration. The higher speed could also be related to some unique propulsion system. The high speeds of Russian attack submarines were meant to counter the advanced propeller cavitation and pump vibration reduction technologies in the US designs, providing them with silent and stealth hiding and maneuvering.
The ALFA-Class of Russian submarines used an alloy of Pb-Bi-45-50 percent by weight cooled fast reactors. The melting point of this alloy is 2570F. They faced problems of corrosion of the reactor components, melting point, pump power, polonium activity and problems in fuel unloading. This class of submarines has been decommissioned.
The nuclear Russian navy also reached its peak at the same time as the US navy. The first of the TYPHOON class (Figure: 9/7) 25,000 ton, strategic ballistic missile submarines was launched in 1980 from the Severodvinsk Shipyard in the White Sea. In the same year, the first OSCAR class guided missile was launched. It is capable of firing 24 long-range antiship cruise missiles while remaining submerged. Five shipyards produced seven different classes of submarines.
The Delta class is nuclear-powered with two VM-4 PWR rated at 180 MWth. There are two-turbine type GT3A-365 rated at 27.5 WW. The propulsion system drives two shafts with seven-bladed fixed-pitch propellers.
The Russian navy has conducted research and experimentation on new types of propulsion concepts. It recognized, for instance, the advantage of gas turbines for naval propulsion and dramatically shifted toward it. Gas turbines offer low weight and volume in addition to operational flexibility, reduced manning levels, and lower maintenance. Even though gas turbines have been used instead of the Rankine Steam Cycle on the nuclear powered ships, they have built fast reactors and studied the use of less reactive lead and lead-bismuth alloys instead of sodium cooling in them. They may also have considered new propulsion concepts such as dissociating gases and magneto hydrodynamic propulsion.
The nuclear powered ECHO II and I can firefight antiship weapons cruise missiles while remaining submerged at a range of up to 100 kilometers from the intended target. These cruise submarines also carry ASW and antiship torpedoes.
Long-term integrity of the compact reactor pressure vessel is maintained by providing an internal neutron shield. (This is in contrast to early Soviet civil PWR designs where embitterment occurs due to neutron bombardment of a very narrow pressure vessel).
5. THE FRENCH NUCLEAR MARINE PROPULSIONS:
France has a nuclear-powered aircraft carrier, the Charles de Gaulle (Figure: 9-8) and ten nuclear submarines (4 SSBN, 6 Rubis class SSN).
The smallest nuclear submarines are the French Rubis-class attack subs, 2600 dwt in service since 1983, and these have a 48 MW integrated PWR reactor from Technicatome which is variously reported as needing no refueling for 30 years, or requiring refueling every seven years. The French aircraft carrier Charles de Gaulle (38,000 dwt), commissioned in 2000, has two K15 integrated PWR units driving 61 MW Alstom turbines and the system can provide 5 years running at 25 knots before refueling.
The Le Triomphant class of ballistic missile submarines (12,640 dwt – the last launched in 2008) uses this K15 naval PWR of 150 MWt and 32 shafts MW. The Barracuda class (4765 dwt) attack submarines will have hybrid propulsion: Electric for normal use and pump-jet for higher speeds. Areva TA (formerly Technicatome) will provide six reactors apparently of only 50 MWt and based on the K15 for the Barracuda submarines, the first to be commissioned in 2017.
The UK has 12 submarines all nuclear-powered (4 SSBN, 8 SSN). The Vanguard Class SSBN, Ship Submersible Ballistic Nuclear (Figure: 9-9) provides the United Kingdom’s strategic nuclear deterrent. The first Vanguard class submarine was launched in 1993 carrying Trident II D5 missiles and is now the cornerstone of the British Defence policy, and significantly contributes to the Alliance’s deterrent forces.
Ballistic missile-submarines must at all times have a robust and reliable link with their chain of command on the mainland. A comprehensive network of communications installations connects Britain’s nuclear fleet with the Commander-in Chief at Northwood, the Secretary of State for Defence in London and the Prime Minister in order to authorize the use of nuclear weapons and keep them under firm political control.
The Royal Navy’s Astute Class submarine (Figure: 9-10) is a nuclear-powered attack submarine that is to replace the five Swiftsure Class submarines launched between 1973 and 1977 and approaching the end of their operational life. In May 2007, the UK MOD awarded BAE Systems a contract to build a fourth Astute Class submarine, HMS Audacious (S122), to enter service in 2013.
In October 2007, Astute made her first dive for an underwater test of systems at the ‘dive hole’ in Devonshire Dock, Barrow. Also in October, the vessel successfully carried out first firing trials from its torpedo tubes.
BAE Systems Insyte (formerly Alenia Marconi Systems) is supplying the Astute combat management system (ACMS). It is a development of the Submarine Command System (SMCS) currently in service in all classes of UK submarines. ACMS receives data from the sonars and other sensors and through advanced algorithms and data handling displays real-time images on the command consoles. Factory acceptance of the operational software was received from the Astute Prime Contract Office in July 2002.
China is understood to have about ten nuclear submarines (possibly 3 SSBN, 7 SSN), similar to the British SSBN and SSN.
China’s naval fleet as of 2008 had five nuclear powered fast attack submarines and one ballistic missiles submarine carrying 12-16 nuclear tipped missiles with arrange of 3,500 km. This is in addition to 30 diesel electric submarines with 20 other submarines under construction.
The Chinese submarine fleet is expected to exceed the number of US’s Seventh Fleet Ships in the Pacific Ocean by 2020.
India launched its first submarine in 2009, the 6000 dwt Arihant SSBN, with a single 85 MW PWR driving a 70 MW steam turbine. It is reported to have cost US$ 2.9 billion, and several more are planned. India is also leasing an almost-new 7900 dwt (12,770 tonne submerged) Russian Akula-II class nuclear attack submarine for ten years from 2010, at a cost of US$ 650 million: the Chakra, formerly Nerpa. It has a single 190 MWt VM-5/ OK-650 PWR driving a 32 MW steam turbine and two MWe turbo-generators.
Brazil’s navy is proposing to build an 11 MW prototype reactor by 2014 to operate for about eight years with a view to a full-sized version using low-enriched uranium being in a submarine to be launched in 2021.
6. ECONOMY OF NUCLEAR MARINE PROPULSIONS:
The cost of building nuclear submarines and aircraft carriers is considered so high that only a few countries have been able to invest in this technology. For instance, the UK rejected the idea of using nuclear power early in the development of its Queen Elizabeth-Class Aircraft Carrier on cost grounds. As a matter of fact nuclear submarines and aircraft carriers were considered to be strategic initiatives, therefore, no considerations were given to the cost associated with the nuclear marine propulsion in the US and Russia. The decisions to deploy nuclear reactors to power ships were based mainly on the following facts that:
- Atomic engines offer exceptional capabilities, which cannot be, achieved with fossil engines; and
- Nuclear reactors offer reliable and compact sources of continuous heat that last for years without needing new fuel. They are well suited for vessels, which need to be at sea for long periods without refueling, or for powerful submarine propulsion.
However, the future designs of nuclear marine propulsion are focused on the overall costs associated with the construction as well as maintenances of vessels.
7. FUTURE TRENDS IN NUCLEAR MARINE PROPULSION:
The following three trends are shaping the future of nuclear marine propulsion technology:
- The All Electric Ships:
All-electric ship propulsion concept was adopted for the future surface combatant power source. It would encompass new weapon systems such as modern electromagnetic rail-guns and lasers under development. To store a large amount of energy, flywheels, large capacitor banks or other energy storage systems would have to be used;
- Stealth Technology:
Tests have been conducted to build stealth surface ships based on the technology developed for the F-117 Nighthawk Stealth Fighter (Figure: 9-11). The first such system was built by the USA Navy as “The Sea Shadow”; and
- Littoral Vessels:
Littoral Combat Ships are designed to operate closer to the coastlines than existing vessels such as destroyers. Their mission is signal intelligence gathering, stealth insertion of Special Forces, mine clearance, submarine hunting, and humanitarian relief.
In November 2010 the British Maritime classification society, Lloyd’s Register embarked upon a two-year study with US-based Hyperion Power Generation, British vessel designer BMT Group, and Greek ship operator Enterprises Shipping and Trading SA “to investigate the practical maritime applications for small modular reactors. The research is intended to produce a concept tanker-ship design,” based on a 70 MWt reactor such as Hyperion’s.
Hyperion has a three-year contract with the other parties in the consortium, which plans to have the tanker design certified in as many countries as possible. The project includes research on a comprehensive regulatory framework led by the International Maritime Organization (IMO), and supported by the International Atomic Energy Agency (IAEA) and regulators in countries involved. In response to its members’ interest in nuclear propulsion Lloyd’s Register has recently rewritten its ‘rules’ for nuclear ships, which concern the integration of a reactor certified by a land-based regulator with the rest of the ship. Nuclear ships are currently the responsibility of their own countries, but none involved in international trade. Lloyds expects to “see nuclear ships on specific trade routes sooner than many people currently anticipate.”
8. FUTURE SUBMARINE FORECE – VIRGINIA CLASS:
The Virginia Class of submarines (Figure: 9-12) represents the future nuclear navy force in the US.
The US Navy plans to develop the Virginia Class into a full modular, all electric submarines that will accommodate large modules to provide interfaces for future payloads and sensors. It is a 30 ships class replacing the Los Angeles Class SSNs possessing the stealth of the Seawolf Class of submarines but a 30 percent lower total cost. It has mission reconfigurable modules capabilities. It is equipped with Unmanned Undersea Vehicles (UUVs), improved sensors, and communication systems. It is characterized with improved habitability and is equipped with advanced strike capability and millions of deployable-networked sensors.
The main propulsion units are the ninth generation GE PWR S9G designed to last as long as the submarine, two turbine engines with one shaft and a United Defence pump jet propulser, which provided 29.84 MW. The speed is 25+ knots dived.
The principal features of S9G nuclear marine propulsion include:
- An all electric ship;
- Enhanced stealth;
- Modular isolated decks;
- Open system architecture;
- Modular Masts;
- Structurally integrated enclosures;
- Mission reconfigurable torpedo room;
- Enhanced special warfare capabilities; and
- Enhanced Littoral performance.
It is designed for mine avoidance, special operations forces delivery and recovery. It uses non- acoustic sensors, advanced tactical communications and non-acoustic stealth. In the future, it will be equipped with conformal sonar arrays. Conformal sonar arrays seek to provide an optimally sensor coated submarine with improved stealth at a lower total ownership cost. New technology called Conformal Acoustic Velocity sonar (CAVES) will replace the existing Wide Aperture Array technology and will be implemented starting in early units of the Virginia Class.
High Frequency Sonar will play a more important role in the future of submarine missions as operations in the littorals require detailed information about the undersea environment to support missions requiring high quality bathymetry, precision navigation, mine detection or ice avoidance. Advanced High Frequency Sonar systems are under development and testing that will provide submarines with unparalleled information about the undersea environment. This technology will be expanded to allow Conformal Sonar Arrays on other parts of the ship that will create new opportunities for use of bow and sail structure volumes while improving sonar sensor performance.