[CrazyIvan]

Gives 10 units to current noise platform. But I think - in the real course of the mission this does not play any role, since these devices are used in the positioning of the ship in a very narrow range of distances - to exit from the sub-base. Actually in the mission - I do not see any real benefit from use APU.

Acoustic signature - can not be changed. If a KILO is working with a diesel engine on snorkeling, the signature will still be the same as in electric motors. Sonalysts programmers, did not think much of this.

Prairie I did in my test tests. It works. But in fact only a few platforms use this. I do not think it's important.
Now - this is solved in a different way, the rate of occurrence of cavitation is increased for these platforms. These ships go at high speed - without cavitation.

For example, a platform without a prairie, starts cavitation at 19 knots, and a platform with a prairie mask, starts cavitating only at its maximum speed 32 knots (add 15 units of noise to the current level)