1. Being far from passive/active decoy is more effective than being close and quiet
2. Passive homing torpedoes can be decoyed only by passive decoy. Launching active decoy gives you nothing in that case.
3. Yes (for someone on opposite side of layer)
4. For all Mk48 in passive its 45 kts (in RA mod)
General rule is: 5 kts lower than maximum attack speed
Im not sure is it simulated in vanilla game.
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