Military & Aerospace

New technologies and trends in Submarines
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Issue Vol. 26.4 Oct-Dec 2011 | Date : 15 Feb , 2012

“At the beginning of the last century, Admiral Sir Arthur Wilson described submarine as underhanded, damned un-English and he suggested that we treat all submarines as pirate ships in wartime and hang all the crew.”

For lower tier navies, nuclear propulsion presents two significant problems. The first is cost. The second hurdle is political. Submarine reactors use weapon grade uranium, meaning any nation wishing to build a nuclear propulsion system must be conscious of world opinion and be a signatory to the Nuclear Non-proliferation Treaty (NPT).

Submarine after all, is the original “stealth technology” for all who go to war under the sea. For the first time in history it played an important role during World War-I. Subsequently, it showed potentials during World War-II and this substantially made the road map to the way wars at sea are conducted. At the turn of century, all submarines used batteries for submerged power. For combined duties of surface propulsion and battery charging, diesel engine is more efficient and was adopted universally. The diameter of the pressure hull of such conventional submarines converged to around 6 m. However even the improved diesels required atmospheric oxygen requiring the boat to either surface or run a snorkel. As such these were prone to easy detection by the enemy radars, infrared detectors and chemical sniffers for exhausts. This stripped the protective cover of darkness from the submarine. It led to nuclear power for propulsion as ultimate solution to true submarine. The pressurized water reactors became the power source for submarines. The commissioning of American USS “Nautilus” on September 30th, 1954 opened a new era.

Compared to other naval platforms, submarines are inexpensive, require few personnel and can hold major maritime assets at risk. With cruise missiles they also can attack targets ashore with precision.

The size of the submarine is driven by the size and weight of the power plant which can reduce the volume available for payload, survivability features and even stealth. In the 50 years of evolution, the diameter of the pressure hull of nuclear submarines increased from 8m to 10.9m and it was realized that a plateau has been reached and the recent boats have been designed with pressure hull diameter of around 9m. It can be said that the diameter of such nuclear submarines of SSN type varies between 8m to 10m. The ballistic missiles pushed the size of the submarines further. For ballistic missiles of range 12000 km of western origin, the diameter of the pressure hull required is around 11 to 12 m for diving depth of around 400m and using hull material as HLES-100 (France), HY-100 (USA, UK) and AB-3 (Russia).

Submarines have been getting bigger and bigger, and which is not good specially from the active acoustic point of view. The primary reason for growth is propulsion technology and size of ballistic missiles.

The bigger size offers higher target strength to the enemy. Within the available technology, materials (HLES, HY-100 or AB-3) and diving depths of around 400m, it is not advisable to substantially increase the pressure hull diameter beyond 12m. This article reviews the growing size of submarines, emerging technologies and recommends not to go beyond the plateau reached in pressure hull diameter for safety, security and operational reasons.

Basic Facts

Submarine is the most cost effective warship. In the peculiar calculus of conflict where costs and benefits are weighed, the existence of a submarine fleet requires an opponent to balance his force equation carefully. Stealth and lethality are factors to be ignored at great peril. Compared to other naval platforms, submarines are inexpensive, require few personnel and can hold major maritime assets at risk. With cruise missiles they also can attack targets ashore with precision.

S-62_Sindhuvijay_Indian-NavThe submarine force can be configured in three distinct areas; first for conventional submarines, second for nuclear powered attack submarines (SSN) and third for ballistic missile submarines (SSBN). While the current generation of combat submarines – both conventional & nuclear – are increasingly difficult to detect and attack, many emerging technologies stand to make submarines of the future quieter and even more deadly. The zone of lethality around a submarine is expanding; cost of underwater endurance is dropping; automation is replacing human expertise; and the number of vendors is certain to expand as third world nations begin indigenous submarine production with sophisticated technology.

It is estimated that about 500 submarines are in active service worldwide in about 30 nations. The significance and need for submarines is being realized by many more nations. Large navies operate large number of units, mainly nuclear. New nations looking for conventional submarines are Singapore, Thailand, Malaysia, Turkey, Portugal, Iran, Venezuela and Vietnam etc. Some nations are developing their first nuclear submarine. Conventional submarines are smaller in size compared to their nuclear counterparts. They are more agile, silent and best suited for operations in coastal and littoral waters where the majority of the world population is living.

Indian-Navy_Akula_K-152Submarines perform a wide range of important tasks in the present maritime environment. More than two thirds of the world surface is covered by seas; over which about 90 percent of trade circulates; it is here that submarines contribute significantly to the freedom of high seas to navigate freely and thus help the humanity. They can effectively counter asymmetric threats, piracy drug smuggling and other organized crime forms. Of course, as a primary role, submarines have extra-ordinary combat capability and they are difficult to trace and overcome.

Conventional Submarines

Concealment and stealth are often signs of guilt especially in small children, and it is not surprising that in the early days of the submarine vessel there was a remarkable amount of moral indignation, perhaps more than any previous weapon of war. At the beginning of last century, Admiral Sir Arthur Wilson talked of submarine as “underhanded, damned un-English and he suggested that we treat all submarines as pirate ships in war time and hang all the crew.”

While the cost of a nuclear submarine may be three times that of a comparable non- nuclear vessel, however when training, crew salaries, life-cycle support and decommissioning costs including safe reactor disposal are added, the cost jumps to around ten times of a conventional submarine.

Diesel engine has been the source of submarine power. Its low weight, compact dimensions, simplicity, efficiency and non explosive fuel are best suited for surface propulsion, generation of electricity and charging of batteries. Although replaced by nuclear energy in large submarines by the 1950s, the diesel continues to be mainstay of medium and small submarines worldwide.

The prime disadvantage of the diesel powered submarines is the need to periodically surface and recharge the batteries used for under water propulsion. In World War-II the Germans designed the Snorkel – a hallow tube raised like a periscope to feed air to the engines. In addition to battery charging, the device also allows the diesel to propel the submarine underwater, conserving the battery charge. However, the snorkel mast creates significant drag and is noisy in operation. This can be heard by sensitive sonars many nautical miles away and snorkel is also detectable by radars. To counter these attributes, modern submarine commanders try to minimize their snorkelling to periods of 20 minutes or less. This is sufficient time to charge their batteries while not giving enemy enough time to detect and engage. During snorkel operations, the exhaust back pressure reduces the efficiency. Turbo charged diesels for submarines have been developed.

Conventional Submarines with Air Independent Propulsion

The need for longer submerged operations resulted in the development and evolution of Air Independent Propulsion (AIP) systems. There are three AIP solutions which are presently operational. Firstly the Royal Swedish Navy and the Japanese Maritime Defence Force have opted for Sterling Engines. They use liquid oxygen and traditional diesel fuel in an inert gaseous environment (helium). Secondly, the French MESMA Steam Turbine AIP has been fitted in last of the Agosta class for Pakistani Navy. In this solution, the turbines burn ethanol with liquid oxygen, requiring exhaust gases disposal that causes noise and bubbles and increases the IR indiscretion rate. Thirdly the Fuel Cells of German origin. These are fitted in German Type 212 A submarines for Germany and Italy. These are also being fitted in Type 214 export submarines. These are polymer electrolyte membrane (PEM) fuel cells. They require storing of potentially dangerous liquid oxygen and a safe metal hydride form of hydrogen. Reformer technology is under development and evolution whereby the hydrogen will be produced on board.

Nuclear Submarines of SSN Type

The advantage of nuclear power for submarine propulsion is complete independence from the surface and enormous high speed endurance. The penalty is complexity and costs of the system. Crew training and retention are vital to successful operations. While the cost of a nuclear submarine may be three times that of a comparable non- nuclear vessel, however when training, crew salaries, life-cycle support and decommissioning costs including safe reactor disposal are added, the cost jumps to around ten times of a conventional submarine.

The zone of lethality around a submarine is expanding; cost of underwater endurance is dropping; automation is replacing human expertise; and the number of vendors is certain to expand as third world nations begin indigenous submarine production with sophisticated technology.

The Pressurized Water Rectors (PWR) have reached maturity. A highly pressurized water loop is passed though the reactor to extract energy which is transferred via a heat exchanger to a secondary loop producing steam which spins a turbine. The steam is condensed and returns to the exchanger.

In a relatively swift development program, USA designed, developed and tested prototype reactors, and installed them on board two submarines. The atomic secrets were shared with the British. The Soviets almost paralleled the American lead. In one stroke, the diesel and battery systems were rendered obsolete for navies who could afford nuclear propulsion.

For lower tier navies, nuclear propulsion presents two significant problems. The first is cost. The second hurdle is political. Submarine reactors use weapon grade uranium, meaning any nation wishing to build a nuclear propulsion system must be conscious of world opinion and be a signatory to the Nuclear Non-proliferation Treaty (NPT).

In the evolution of US nuclear program, Submerged displacement rose from 3075 tons in Skipjack to 6926 tons in Los Angles to 9150 tons in Seawolf with plateau reached and now down to 7800 tons in Virginia class. A similar growth pattern can be seen in succeeding classes of other navies nuclear submarines as well. The increased displacement requires the corresponding increase in horse power, a bigger propulsion plant which in turn requires a bigger boat, and thus a self-sustaining cycle of growth is established.

In keeping with the available high strength steels (HLES, HY, AB series), and the desired diving depth, the diameter of SSN submarines has varied from 8 m to 10 m approximately. Submerged speeds of 30 to 35 knots have been achieved.

Nuclear Submarines of SSBN Type

Since 1960, the US started putting ballistic missiles on board submarines called boomers. The technology of the Ballistic Missile development grew in leaps and bounds. Today, the US ballistic missiles of 12,000 Km range have been evolved in reasonable compact dimensions. Other nations have developed ballistic missiles of ranges varying from 6000 to 10000 Km.

US-Nuclear_SeawolfThe size of the SSBN nuclear submarines are determined by the size of the ballistic missile and the numbers carried on board. In the SSBN type nuclear submarines the diameter of the pressure hull has been around 11 to 12.m.

This is to suit the fitment of the ballistic missiles, to match the properties of existing available high strength steels, to match the desired diving depth, to keep the target strength minimal possible and to be economical and efficient.

Ballistic missiles will continue to be developed by many nations and for maritime deployment the envelop of SSBN Type nuclear submarines now under operation will have to be kept in mind. Any attempt to considerably increase the pressure hull diameter could be counter productive as one will be operating in areas of the unknown and make oneself an easy target for the enemy.

Conclusions

It was alleged that on March, 2010, in Yellow Sea, a torpedo from a conventional and very old submarine belonging to North Korea, sunk a modern ASW Corvette of the Republic of Korea Navy with a loss of 46 sailors. Let it be known that the conventional submarines with batteries & diesel engines will continue to pose threat and combat potential. The AIP systems will reach maturity as experience is gained in exploiting conventional submarines. More and more nations will acquire such submarines. These submarines have converged to optimum pressure hull diameter of around 6 m.

Editor’s Pick

Very few nations possess nuclear powered submarines (SSN type). The cost and complexity of nuclear submarines are prohibitive. The realization on the initial cost, crew training, life cycle exploitation and support and decommissioning including safe reactor disposal etc, discouraged the Canadians to go for nuclear fleet. The number of nations who will adopt such costly and complex systems will be few and far between. However the combat potential of the nuclear submarines (SSN) will remain superior. The plateau has been reached in the size of SSN submarines and the optimum pressure hull diameter has converged to around 8 to 10 m.

Any future SSBN submarine will have to be designed within the proven envelope so as to remain in the realm of the known.

Fewer nations have designed and built SSBN type nuclear submarines. The size of such submarines is dictated by the size of the ballistic missiles. The search for technology to design and develop smaller size ballistic missiles for equivalent range is continuing. Presently the existing SSBN type nuclear submarines have optimum diameter of their hulls around 11 to 12 m. This has been possible within the available high strength steels and desired diving depths. The envelope of the recent modern SSBN type submarines has been evolved on full consideration of combat potential, target strength and other vital design and operational parameters. Any future SSBN submarine will have to be designed within the proven envelope so as to remain in the realm of the known. Any attempt to substantially further increase the diameter of the pressure hull to accommodate larger size ballistic missiles could lead to unforeseen problems.

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The views expressed are of the author and do not necessarily represent the opinions or policies of the Indian Defence Review.

About the Author

Vice Adm Rajeshwer Nath

Vice Adm (Retd) Rajeshwer Nath.

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