Submarines Noise levels

It is easier and cheaper to sink an  aircraft carrier . Than to allow  it's planes to fly around . Submarines can keep an aircraft carrier at a distance .  But why do submarines still fire torpedo ?  This in my view  has disadvantages . Even if submarine is undetected , and fires torpedo . Then noise from torpedo , will identify the position of submarine . Range of torpedo is relatively small . Allowing a small search area to be set up , by anti-submarine  forces .

Why not use torpedo tube  to launch anti-ship cruise  missiles . They can be launched from much greater distance . Second the launch is less noisy and less likely to give position of sub away . And even if launch position becomes known , the search radius is greater . Allowing sub more time to escape  . And finally  the cruise missile is faster and  more difficult to intercept  than torpedo .

Locating a surface fleet , can be done by sub itself . Even if ships have engines shut down . And acoustic long range detection is not possible . Drones can be launched by sub . To search surface  . Sending real time info back to sub . Once ship located , then missiles launched . Flight time to target relatively short , allowing cruise missile to do a search pattern near target , before it escapes .

Torpedoes can't be shot down by air defence systems... and in terms of sinking even very large ships they are the best solution.

For use against ships the torpedo is designed to go under the ship and detonate... generating an enormous bubble of gas... which of course rises up and lifts the ship out of the water. But look at any ship in a dry dock... if you only supported their weight in one position or lifted them with one crane then they would break in half at the point of lift.

That is what happens when the bubble of gas lifts the ship... it breaks the back and when split in half no ship would remain on the surface.

There is a saying that torpedoes let water into the hull of a ship while anti ship missiles let in air in the top.

Not strictly accurate, because AShMs let fire into the ship which can be worse than letting in water...

And some torpedoes have ranges of 50km+.

For areas where enemy ships have to pass you could also lay mines too.

For use against enemy subs the Russians have developed versions of the Club missile that is a Mach 2 or Mach 2.5 ballistic rocket that flies a simple path to where the enemy sub is located to drop a torpedo into the water to then engage the sub. The rocket is faster than anything moving through water and much quieter, and when used against subs there is no air defence system to worry about.

Against a ship it would be much less effective.

There is no reason why a torpedo could not initially operate at a fairly low speed limiting the noise it generates to begin with and then accelerate as it gets closer to the target.

I think the main point is that if you detect an incoming torpedo from 20km range you wont be manouvering to launch an anti sub weapon to engage the sub, you will be manouvering your ship to make yourself the smallest possible target and to leave the danger zone while you work out if it is heading towards you or one of the other ships you are with...

If it was an anti ship missile then you would activate all your radar and SAMs and CIWS and prepare to launch decoys and jammers etc etc to defend the ship and pass on information to other ships nearby to do the same.

There is rather less they can do in the case of an incoming torpedo to be honest...

Good of the Russians to think about this . So it looks like the fastest means of delivery is a rocket . The best type of warhead is a  underwater  type . And best detection depends on resources  . Sattelites launched in LEO for this particular case , may provide best and most updated info on location of fleet . If not available  , then long range over horizon radar . If not then long range sonar . If not then long range surveillance  drone .

But I thought , probably the cheapest system , is one that does everything itself . A low RCS , high altitude and long range drone / missile / torpedo  , can fly without GPS , detect without radar or sonar . On locating target , it can shed engine and wings , then fire rocket . Approach fast . Near target dive into water.  And activate below water mark . No need for sattelite , anti- sattelite , ship , sub , radar , sonar ......... like flying fish .