So, you wait for war to come and turn off the noise? Really??? That does not make sense to me at all.
It does not.
Obviously you have no clue to use of deception in masking sound signature in navy ships. Gathering individual ship's sound signature is a modern day version of those old days photo-recon of enemy ship silhouette. With a data bank of ships sound signatures, a sonar operator can recognise an individual ship and whether it is freind or enemy.
To counter such intelligence gathering in peace time, it is normal to mask actual sound of a ship by generating fake sounds, and noise maker is one such device. In war time, turning off the noise maker, or altering the previous sound render enemy's sound signature data useless and make sonar operator's work harder.
Actually, it is
YOU who do not have that clue.
Masking is not the same thing as silencing. Surface ships on the move cannot suppress their noise, however, they can mask their signatures. Both signatures can have the same noise level with one signature the true one belonging to the ship.
On the other hand, subs belongs in a different issue. A sub tries to be as silent as possible at all times. No masking. If a sub cannot be detected, then it does not matter its signature. But if a sub continues to produce masking noises that are greater than its true signature, it can be tracked, so what good is it then? You can try to argue that producing a louder but false signature during peace time to deceive potential adversary is a 'valid' tactic but then it begs the question of why bother to design subs to be as silent as possible in the first place?
This lead us back to the issue of being silent. If you cannot produce a sub that is superior to the enemy, then it does not matter if you mask your true signature or not. As long as you are on the move, trying to mask your true signature is pointless, you will be tracked with that false signature
AS IF it is your true one. Turning it off does what? Nothing. Your true signature is just as loud. So what if the enemy detect a supposedly 'new' signature? Do you think he cannot deduce the fact that the new signature is in the same position as the old and most likely that mean you? If the new signature does not match known 'friendlies' what does that make the new signature? How about you being a 'foe'? What good was your masking then?
Another clue for you: Radar detection and sonar detection are 99.999% philosophically identical. EEs from one discipline can transition to the other with little trouble. In radar detection, the F-22 flies with enhancers primarily to assist air traffic controllers with the secondary benefit of masking its true RCS. Underwater, there are no traffic controllers, so even if the sub's masking signature is as low noise level as the true, if the false is finally detected, the true will eventually be figured out and that deduction will be without your knowledge, in other words, if the enemy figured out your mask, he will do whatever he can to convince you of your perceived advantage to keep you in the dark of his advantage.
This is why your friend's claim to have worked on sonar is getting more dubious upon closer examination of his statement that a sub
MUST employ masking techniques.