Attack submarines are the most vital weapons of every navy.
The modern attack submarine is, in fact, a wolf that hunts alone. Apart from protecting surface ships and convoys, they are the nightmare of every surface platform with their primary mission of stealth attack; and of coastal and deep land targets with their long-range cruise missiles.
We can examine modern attack submarines in 3 different categories in terms of their propulsion systems:
1. Diesel engine/diesel generator: These move with their diesel engines on the surface (and at depths close to the surface - snorkel depth). They also charge their batteries with a diesel generator. They are driven silently while submerged with their lead-acid batteries. In the newest models of these, their lead-acid batteries are evolving into much more efficient Li-Ion batteries.
The speed of submarines with lead-acid batteries does not exceed 20 knots while submerged. They also quickly consume the battery at this speed. Their duration at depth is measured in hours; at economical speeds, a few days. Li-Ion battery submarines can stay at depths for 1 week-10 days and can move at high speed in an emergency. Japanese Taigei submarines are a good example of this.
2. Air-independent propulsion submarines. (AIP ): The best example of these is the Reis Class submarines. These submarines produce electricity while submerged with hydrogen fuel cell technology and Proton Exchange Membrane, keep the lead-acid batteries constantly charged and can stay underwater for 2-3 weeks without surfacing. However, they make 4 knots economically and 8 knots at high speed. If they move at 20 knots, there is no difference from the diesel submarine above as they would deplete their batteries. When the AIP and PEM systems are not working, they are standard diesel-powered submarines.
3. Nuclear-powered submarines: These are submarines that are propelled by a small nuclear reactor and can move silently with the electricity provided by this reactor; in addition, they can stay underwater for months by obtaining oxygen from the water with this electricity. However, they have dive times that do not exceed 90 days in terms of the food they can carry. Also, since the psychological health of the crew is taken into consideration while submerged, very long dives are not made. These submarines can reach speeds of 30+ knots underwater. Since the reactor can theoretically operate for decades (20-30 years), it is possible for these submarines to operate for a very long time without stopping at a port.
Japanese Soryu class submarines were AIP submarines. However, they produced the last 2 submarines as Li-Ion class. And they are producing the last Taigei class with Li-Ion propulsion too.
Japanese submarine captains complained about the slow speeds of AIP submarines, emphasizing the importance of getting away from the area they are in quickly, after using torpedoes, and in an emergency, and as a result, the Japanese Navy turned to the Li-Ion system in its new submarine concept.
Inspired by the Japanese, we are also studying developing a Li-Ion propulsion system. Although AIP propulsion is planned for Milden, the complexity and external dependency of this system may push us towards Li-Ion powered submarines.
Although nuclear powered submarines seem to be the Nirvana of this business and these submarines can go much faster and dive deeper, the fact that the reactor is constantly running means that many pumps and mechanisms produce noise. In this respect, modern Li-Ion and AIP powered submarines are quieter. These features have been highlighted many times in naval operations.
Underwater when you need speed use Li-ion batteries, when you just need cruising or approaching the territory of missionswitch to fuel-cell hydrogen.
Yet we have got a lovely bulkhead (well - isolated) that keeps it away from operations center.
