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How HSMS Gotland, A Small Swedish Diesel-Powered Submarine, Sank USS Ronald Reagan

The United State military has the strongest and most diverse navy in the world. The United State militaries fleet of aircraft carriers is so large, it makes the US Navy the second the second largest Airforce in the world, second largest to the actual  US Airforce. A single Nimitz class aircraft carrier like the USS Ronald Reagan a 6.2 billion dollars nuclear-powered ship can carry the twice aircraft as any other foreign carrier. Which makes it even more shocking that it was sunk by a single diesel-powered Swedish submarine during a war game in 2005.

How That  HSMS Gotland Sank USS Ronald Reagan?


A single submarine that cost the same as an F-35 at 100 million dollars managed to sneak by an entire carrier task force with anti-submarine defences and not only that it also managed to enter the red-zone and score multiple torpedoes hits on the USS Ronald Reagan, sinking it virtually, before shrinking back into the vast Ocean undetected. This is just one of many exercises where the Swedish Gotland class submarine proved too stealthy for the world's strongest navy. The new submarine proved so threatening that the US military leased the Swedish submarine for an additional year to develop a strategy to counter the silent threat. 


 So all the science thinkers let's get to the Answer, what set the Gotland apart from other submarines.  Submarine's primary instrument to detect enemy's submarines is  sonar. Sonar essentially a finely tuned air that works like whale's or dolphin's echolocation to create a 3D map of ocean around it. There is an active sonar where the submarine will send out a sound pulse called a ping and listen to the reflections. But in the warfare, this is not a sound strategy as that ping is detectable by enemies to give your exact location. So passive sonar is used where no ping is emitted instate you only listen. These electronic ears are so accurate that the nationality of submarines can be determined based on the operating frequency of the alternating current used in its power systems. The 60Hartz alternating current of an US submarine could be differentiated from the 50Hartz of European submarine If the transformers and other electronics were not adequately insulated from the hall.  The Swedish managed to create a submarine so silent that it was practically undetectable by passive sonar. 




Now the question is how did Swedish manage to make such submarine at such low price?


The Gotland is the first submarine in the world to use a Stirling engine as it's power generator.  Stirling engines are not a new concept with the first being created and patented by Robert Stirling in 1816. Inspired by a series of high-pressure steam boiler explosions at the beginning of the industrial revolution. Robert Stirling wanted to create a safer engine that did not require such high pressure. He did this by creating a fixed mass of gas permanently sealed within. Here one side of the piston, cylinder has a large buffer space which allows for a relatively constant pressure on the other side of the piston while the other side fluctuates in pressure due to alternating heat cycles. When heat is applied to the outside of the cylinder, the pressure increases causing the piston to move until the pressure equalizes.  Now if we cool the outside of the cylinder with a heat exchanger, the pressure will drop and once again the piston will move. This is our basic pressure cycle to create mechanical work. But this is an insanely inefficient system, as most of the energy we put into the system as heat is lost during the cooling cycle, not to the gas, but to the actual cylinder wall which provides no mechanical work. Robert Stirling solved this by adding a displacer piston which can drive the gas from one end of the cylinder to the other. Allowing this end to be permanently hot and the other permanently cold. So the cylinder wall is no longer experiencing a temperature cycle. The pressure cycle here works slightly differently. First, the air in the hot end expands and causes the displacer to move into contact with the power piston, displacing more air from the cold end to be heated and expanded, allowing work to be done on the piston. The air on the hot end now has nowhere to go so it's driven to the cold end where it is cooled and contracts causing work to be done once again on power piston. This is our new pressure cycle. The efficiency of this system can be increased further by placing what is essentially a heat battery in the tube between the hot and cold cylinder. This conserves a huge amount of heat that would otherwise be wasted during the cooling cycle and gives the heat back to the air as it travels back through. Robert Stirling dubbed this through a regenerator. Now we have the foundations of a useful engine. By incorporating a cooling system and a heating chamber we create a large temperature differential to drive the engine and the efficiency can be future increased by increasing the number of tubes connecting the hot and cold spaces along with the number of regenerators and adding fins to increase the surface area of these tubes to allow for heat transfer. 


Sterling engines ultimately fell into obscurity as stronger steel became available to make steam engine boilers safer but have seen a resurgence in recent decades with the Gotland being the most famous implementation. The Gotland uses two Stirling engines that use diesel and liquid oxygen to provide heat which in turns it's 75 kW generators. These generators can run an electric motor directly or charge batteries that can provide a huge boost in speed when needed. All the while, the exhaust is compressed and stored onboard, allowing the submarine to stay submerged up to 2 weeks vastly longer than any other diesel-powered submarine. 


 So why is it so silent compared to other submarines? It actually doesn't require much explanation as to why an internal combustion engine using tiny controlled explosions for power tends to cause some noise. While the multi-billion dollar nuclear-powered submarines need to pump huge volumes of coolant to their reactors to prevent a meltdown causing enough noise to be detectable by passive sonar within a certain range.  


Well, this is the fascinating application of the laws of thermodynamics. Understanding and applying the laws of science is the closest to a real-life superpower in this world.                     
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