Aug 31, 2021 09:50:00

What is the difference between a nuclear submarine and an air-independent propulsion (AIP) submarine?

Submarines are primarily powered by diesel and nuclear engines, and

air-independent propulsion (AIP) engines were put into practical use at the end of the 20th century. Nuclear engines are superior in many respects except for costs, but technological advances are closing the gap between AIP and nuclear engines.

Air Independent Propulsion Could Create Silent Killer Submarines | The National Interest
https://nationalinterest.org/blog/reboot/air-independent-propulsion-could-create-silent-killer-submarines-192514

A conventional diesel engine-equipped submarine (diesel submarine) uses a diesel engine to generate electric power to power propellers and systems, and when diving, it navigates with the electric power stored in the battery. However, running a diesel engine is noisy and requires limited air in the water, so it needs to surface and recharge frequently.

Nuclear submarines (nuclear submarines) that appeared in the 1950s are superior to diesel submarines in terms of sustainability, stealth, and speed due to their characteristics of 'high quietness,' 'does not consume air,' and 'high output.' , The US Navy has completely abolished its diesel submarines and replaced them with nuclear submarines. However, due to cost issues, most other countries have introduced nuclear submarines but still have diesel submarines.

The concept of AIP dates back to the 19th century, but the Swedish Gotland-class submarine, which was put into service in 1996, was the first practical example of an AIP engine-equipped submarine (AIP submarine). The AIP engine introduced in the Gotland-class submarine is a Stirling engine, which is a heat engine that combines liquid oxygen and diesel fuel.As of the 21st century, three systems including fuel cells and closed-cycle steam turbines are used as AIP engines. .. In Japan, 10 out of 12 'Soryu- class submarines' are equipped with Stirling engines.

The US Navy was the only one to completely replace it with a nuclear submarine because of the great cost issues. The Virginia-class ship, which the US Navy has been operating since 2004, costs $ 2.6 billion (about 286 billion yen). On the other hand, the construction cost of AIP submarines is generally 200 million dollars (about 22 billion yen) to 600 million dollars (about 66 billion yen), so four AIP submarines can be deployed with the budget of one nuclear submarine. The main difference in cost is that the nuclear reactor is expensive, but while many nuclear submarines are large ships with more than 100 people on board, AIP submarines are small ships with 30 to 60 people. There is also the difference that there are many medium-sized ships. Of course, the small size of a submarine does not mean that the attack power of torpedoes and missiles is low, but large ships can be equipped with weapons such as a vertical launch system.

Also, the speed is increased because there is a big difference between the nuclear submarine and the AIP submarine. Speed is related to strategic maneuverability and tactical agility, but high-speed navigation is a source of noise, so it is unlikely that you will sail at maximum speed even in a submarine.

In the case of the attack type nuclear submarine operated by the US Navy, it is possible to maintain 30 knots (approximately 56 km / h) or more during the dive. On the other hand, the German Type 214 submarine, which is the representative of AIP submarines, is 20 knots (about 37 km / h). However, the cruising speed of AIP itself is slow, and in the case of the Gotland class in Sweden, the cruising speed to maximize action sustainability is about 5 knots (more than 9 km / h), aimed at water movement and long-distance movement. Considering the navigation speed, it is extremely slow. This is because AIP cannot generate enough power for high-speed navigation, and AIP submarine is equipped with a diesel engine to supplement the speed.

One of the important points in the operation of submarines is stealth and quietness. Just as the British nuclear submarine ' Vanguard ' and the French nuclear submarine ' Le Trionfan ' collided in 2009, the stealth of the nuclear submarine is 'a level that is not noticeable to each other'.

AIP submarines, on the other hand, are thought to be even more stealth if properly designed. This is because the hydraulic system makes noise even in a nuclear engine with less noise, while the AIP engine is virtually silent. Diesel submersibles also exhibit quiet performance comparable to AIP submersibles when driven by batteries, but the drawback is that the drive time is several hours. AIP submarine can maintain this quiet performance for several days.

One of the merits of nuclear submarines is that, in theory, you can dive for 3 to 4 months in a row. As mentioned earlier, old diesel submarines had to surface every few hours to days to charge the battery. On the other hand, the ascent interval required for AIP submarine is 2 to 4 weeks. Nuclear submarines have an overwhelming advantage in long-distance diving, but when there are many friendly ports near active sea areas such as Japan, China, and Germany, this action endurance is not a high priority. Is being considered.