Design where Neptune: fears to tread.
Thomas Withington, inputs from Eric H. Biass
A coustic signature reduction techniques have steadily become more advanced and gradually less expensive throughout the history of the submarine and since the invention of sonar during the first decade of the twentieth century. Similarly, military electronics have become smaller and cheaper thanks to Moore's Law--the principle by which the number of transistors that can be placed onto an integrated circuit doubles every two years. The result is that many advanced fire control and sonar processing systems absorb less space and can be installed at a lower cost inside a submarine.
Notwithstanding these important developments, this revolution has arguably been led by the evolution of air-independent propulsion, which allows a submarine to quietly patrol for long periods, albeit with the trade-off of a slower speed, and dispenses with the erstwhile snorkel which in the past provided antisubmarine aircraft with a useful indication vis-a-vis their quarry's location.
The anaerobic technique is also notably cheaper than a nuclear reactor, which costs around $ 100 million in the case of the US Navy's nuclear ballistic missile and attack submarines. As a comparison, the Module d'Energie Sous-Marine Autonome (Mesma/Autonomous Submarine Energy Module) devised by French shipbuilder DCNS is reported to cost around $ 60 million per unit.
The American Case
Although air-independent propulsion has heralded a quiet--in many senses of the word--revolution in submarine propulsion, nuclear power is still the propulsion system of choice for the US Navy. The force is busy reorienting its submarine force to meet the challenges of asymmetrical warfare on the high seas. This reorientation has included the re-rolling of four Ohio class ballistic missile nuclear submarines (SSBNs) away from their traditional role of supporting the subsurface component of the United States nuclear deterrent.
These four Ohio boats--USS-Ohio, USS-Michigan, USS-Florida and USS-Georgia--can each carry up to 154 Raytheon BGM-109 Tomahawk cruise missiles in 22 of their 24 former Lockheed Martin UGM-133 Trident-II nuclear-tipped ballistic missile launchers. The remaining two missile tubes have been converted for use by special forces and for the launch and recovery of underwater drones, which can be used for mine-countermeasures work and also for reconnaissance of coastal areas to support covert special operations.
All of the Ohio class boats, including both the ballistic and cruise missile platforms, will start to be decommissioned from circa 2029. This will mean that the US Navy will have a corresponding requirement for a replacement SSBN. To this end, the US Navy's SSBN-X initiative could yield a design costing around $ eight billion per boat compared to the approximately $ two billion unit cost of the existing Ohio vessels.
In terms of design options, a modified version of the navy's existing General Dynamics Electric Boat and Northrop Grumman Newport News Virginia class nuclear attack submarines has been muted. So far, seven Virginia class boats have been commissioned. Delivery of the USS-California, USS-Mississippi, USS-Minnesota, USS-North Dakota and USS-John Warner is expected by 2015.
Eventually, these boats will replace the US Navy's current Los Angeles class hunter-killer submarines. Ultimately, the service may acquire up to 30 Virginia class examples.
One of the remarkable aspects of the Virginia design is that it is the first American submarine conceived for the post-Cold War world. In principle, this means that a number of distinct design features have been rolled into the vessel, including intelligence-gathering and mine counter-measures capabilities, plus special forces support along with the traditional 'bread and butter' missions of anti-ship and antisubmarine warfare.
Displacing 7800 tonnes when submerged, the Virginia design calls on modular deck structures that are mounted on cushioned housings and installed as a single unit. These housings help to reduce the submarine's acoustic signature, as do the anechoic coatings on the hull and the vessels' propeller design. This propeller is driven by a General Electric S9G pressurised water reactor, which has the same lifespan as the submarine, and can drive the boat at speeds in excess of 25 knots when dived. In terms of depth, the submarine can reportedly navigate to below 243 metres.
The US Navy is not the only force receiving new nuclear-powered hunter-killer boats. BAE Systems received the go-ahead to construct a fifth Astute class vessel for the Royal Navy on 1 June 2010. The first boat in the class, RMS-Astute, was launched in 2007 and the class will replace the erstwhile Swiftsure boats which have been operated by the Royal Navy since the mid-1970s. Coastal strike is one of the missions that these boats will perform and. to this end; they can fire Tomahawk Block IV land attack missiles from their 553-mm torpedo tubes.The six tubes that adorn the vessel can also fire BAE Systems Spearfish torpedoes and deploy mines.
The machinery for these vessels include a Rolls-Royce PWR-2 pressurised water reactor; the powerplant developed for the Royal Navy's Vanguard class ballistic missile nuclear submarines which will not require refuelling during the submarine's life. The reactor provides power for the single shaft, and also for the Rolls-Royce pump jet propulsors.
France and Mesma
France is, together with the United Kingdom and the United States, the only other western country that designs and builds nuclear submarines. This year, the French Navy commissioned its fourth and final 'Le Triomphant' class SSBN into service on 20 September 2010 with little fanfare, preferring to keep these boats and their deadly cargo under wraps.
The Le Triomphant boats are one component of a wholesale modernisation of the navy's nuclear submarine force, which will also see the induction of DCNS' Barracuda class nuclear hunter-killer boats as a replacement for the Rubis class which have been in service since the early 1980s. Along with other submarines, the Barracudas will be equipped with MBDA's Scalp submarine-launched surface-to-surface missile with a range of around 1000 km.
The first boat, the Suffren, is expected to enter service in 2017, with the commissioning of all six vessels completed by 2027. One of the interesting features of the Barracuda boats is that their high level of automation reduces their crew to 60, compared to the 78 required by the preceding class. In terms of performance, these boats will be able to dive to depths in excess of 350 metres, and maintain a speed of circa 25 knots.
Technology developed for DCNS' Le Triomphant and Barracuda boats has been leveraged into the company's Scorpene class conventional vessels that have in turn been co-developed with Navantia of Spain (the scorpaenidae family of fish includes the scorpene, or scorpion fish in English). The firm claims that the Scorpene design is the most modern conventional submarine on the market. In total, 14 have already been ordered by Chile, Malaysia, India and Brazil and four are already in service with the first two countries.
Fitted with the Mesma system, they can remain submerged for more than three weeks and remain at sea for around 240 days. They take benefit of research made on their nuclear forebears, particularly in terms of acoustic discretion and sonar performance. Furthermore, high-tensile steel has been used in the boat's construction, allowing unlimited dives to the vessel's maximum depth, while reducing the weight of the hull and freeing additional space for fuel and ammunition.
Other conventional boats in the DCNS catalogue include the Agosta-90B diesel electric design. Joining France and Spain as an Agosta customer, Pakistan has purchased three examples that are locally known as the Khalid class. The lead boat, the Khalid, was constructed at DCNS' shipyard in Cherbourg on France's western coast, with the Saad and Hamza built at Karachi Naval Dockyard. The Hamza was outfitted with DCNS" Mesma system and Pakistan has ordered this propulsion system for retrofit on its other two vessels.
Delivery of the Mesma kits is expected by 2011. This equipment provides these vessels with up to four times the submerged endurance of a traditional diesel submarine.
Other conventional designs are under consideration by the company, which is also moving ahead with its Andrasta concept to develop a boat with a reduced procurement cost compared to existing conventional boats. Optimised for coastal operations, this boat is intended to perform patrols of around two weeks' endurance, and will be able to carry six heavyweight weapons. The baseline design is less than 50 metres in length, which helps to improve manoeuvrability to reduce signatures and will allow the vessel to loiter on the seabed.
Looking further into the future, DCNS took the opportunity of presenting its SMX-25 concept prior to the 2010 Euronaval exhibition in Paris. The boat is designed to address the slow transit speeds of conventional submarines, which are limited in this regard. To solve this problem the SMX-25 would perform a fast transit on the surface at a maximum speed of 38 knots using three gas turbines and three water jets, with two electric pods Tor submerged navigation, and then submerge to perform its mission in the patrol area.
Surface displacement of the SMX-25 design is 2850 tonnes, and 4500 submerged. Its weapons load-out includes up to 16 vertically launched missiles and four torpedo tubes.
Following the example of the DCNS Agosta design, air independence is also a key part of Kockums' A26 submarine. This Swedish shipbuilder is developing the A26 as an improved version of the Gotland class boats; three of which have been operated by the Swedish Navy since the mid 1990s.
The new A26 vessels, which displace 1830 tonnes, will use a Stirling-engine-based propulsion system. The engine uses a diesel and liquid oxygen and is coupled to a 75-kW generator to recharge the submarine's batteries and which also provides propulsion. Another notable feature of the boats is their relatively light manpower requirement of up to 26 personnel, which helps to keep running costs down.
Perhaps mirroring the reputation that Swedish cars have for safety, the A26 has been engineered to have a high degree of resistance to shock and underwater explosions, along with a highly stealthy design in terms of radar and acoustic signatures.
Like Kockums. Navantia of Spain has emerged as a growing force to be reckoned with in the field of conventional attack submarines. The company is currently developing its Hydrogen-based air-independent propulsion S-80 boat. This boat is intended to launch Boeing UGM-84 Harpoon anti-ship and land-attack missiles, cruise missiles and heavyweight torpedoes. The S-80 has been developed for a Spanish Navy conventional air-independent propulsion attack submarine requirement, for which design work commenced in 2002.
The force is expected to acquire a total of four boats, with the service entry of the first example expected in 2013. Displacing up to 2426 tonnes submerged, the boat will be capable of twelve kt when on the surface and 19 kt underwater. The S-80 design features some remarkable additions, such as the use of glass-reinforced plastics for the vessel's superstructure, while a sail designed with sloped sides helps to reduce the boat's acoustic signature.
Joining Navantia and DCNS as one of Europe's most successful submarine producers is Germany's Thyssenkrupp Marine Systems, whose Type 214 design has been ordered by Greece (six boats), South Korea (three boats), Turkey (six boats) and Pakistan (three boats). Essentially, the Type 214 is an improvement on the legacy Type 212 boats produced by Howaldtswerke-Deutschc Werft (now part of Thyssenkrupp), four of which were acquired by the Deutsche Marine (German Navy), with an additional two vessels to be delivered by 2013.
Two Type 212 submarines have also been acquired by the Marina Militare (Italian Navy), with an additional two boats to be delivered by 2016. Compared to the proton exchange membrane hydrogen fuel-cell-powered Type 212, the polymer electrolyte membrane hydrogen fuel cell-powered Type 214 can dive down to over 400 metres and has a range of 22,224 km compared to the Type 212's 14,816 km.
Away from Western Europe, despite having witnessed a decline in its national submarine fleet, Russian shipbuilders are still able to design robust underwater vessels. For example Rubin, in conjunction with Fincantieri of Italy, has developed the S-1000 class boat, which is closely based upon the Amur class conventional submarine (see below). The former appears to use a chemical-oxygen air-independent power-generating source. With a top speed of 14 knots, she can deploy DCNS/Whitehead Alenia Black Shark heavyweight torpedoes and Novator 3M-54 Klub (Nato reporting name 'SS-N-27 Sizzler') cruise missiles.
Although it has languished for some years following the end of the Cold War, the Russian Navy is beginning to once more invest in its submarine capabilities, commissioning its first oxygen-hydrogen fuel-cell Lada class vessel, the St. Petersburg. These new conventional boats are tasked with anti-submarine and anti-surface warfare, along with the collection of intelligence.
The boat's torpedo tubes are fed by weapons loading equipment which helps to further reduce the vessel's acoustic signature, which is reportedly notably less than that of the Russian Navy's Project 877 Paltus conventional hunter-killer boats which the Lada class vessels succeed. Along with launching torpedoes and cruise missiles, these tubes can also be used for the delivery of marine special forces. The 2700-tonne Lada boats require an overhaul every ten years, and dock repair every 2.5 years.
The export version of the Lada class is the Rubin Design Bureau Amur-950 concept. This design has ten vertical launch tubes for cruise missiles and four 533-mm torpedo tubes. Capable of a maximum diving depth of 300 metres, the Amur-950 vessels have an endurance of up to 30 days and a 20-kt submerged top speed, plus a complement of 18.
The Rubin Design Bureau is also responsible for the Amur-1650 conventional submarine. Compared to the Amur-950, this design has slightly more capability, with six 533-mm torpedo tubes and a fully submerged speed of 21 kt, although its maximum diving depth remains the same. Compared to its sibling, it can also operate for 45 days, although it has a larger crew of 35 individuals.
In terms of future design trends, navies themselves tend to be reticent to discuss the type of capabilities that will be rolled out onto future submarine classes. Nevertheless, subsystems manufacturers such as Sargent Aerospace and Defense of the United States, which has been involved in hydraulic control design and manufacture since the days of the first operational nuclear submarine USS-Nautilus (commissioned over half a century ago in September 1954), gave the author insight into the trends it has witnessed over its 50 years of involvement in the submarine world.
These trends have included an ever-increasing array of payloads carried by submarines. This is perhaps best illustrated by the Virginia class boats that are entering US Navy service (see above). Acoustic and radar signatures have been increasingly better managed, while manpower levels are reducing and boats benefiting from growing levels of electrification and digitisation.
There is every indication that these trends will continue well into the future as submarine technology develops further, ensuring that these vessels are no longer just a 'must have' asset for the world's richest navies, but become de rigueur for such forces the world over.
RELATED ARTICLE: SSBN?
In this somewhat dated acronym, the two 'S' stand for 'submersible ship' when, oddly enough, all submarine sailors are adamant to call their vessels 'boats'. The 'B' stands for 'ballistic (missiles)', while the 'N' denotes nuclear (powered). They are vernacularly referred to as "Boomers". The French equivalent of the acronym, SLNE, means 'sous-marin nucleaire lanceur d'engin', where 'engin' (literally 'device') is a euphemism for ballistic missile. In both cases, the 'N' only refers to the propulsion mode, not to the tip of the missiles.
In a nutshell, the propulsion system pioneered in the Scorpene combusts a mixture of compressed oxygen and ethanol at 60 atmospheres. The resulting steam then powers the conventional turbine. As the combustion of the oxygen and ethanol occurs under pressure, the resulting carbon dioxide, which occurs as a bi-product to this process, can be expelled from the submarine even when operating at depth without the need of an exhaust compressor.
A Stirling engine, as used by Kockums, contains a fixed quantity of a gaseous fluid, in this case liquid oxygen. This is contained in two chambers, each housing a piston. Both pistons are connected to the same crankshaft. One chamber is surrounded by a heat source, while the other is cooled. As heat is added to this chamber, the gaseous fluid expands which forces the piston to move upwards. However, as the piston moves, it sucks in cooler gaseous fluid out of the second chamber forcing this piston in this chamber downwards. The rush of cooled air into the heated chamber reduces the internal pressure causing its piston to fall. This cooler air in the heated chamber then rises in temperature and pressure, and the process is repeated.