“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.

The 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.

Submarines 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.