A simple and common defensive missile warhead, whose history dates back to the times of early submarines. Decoy Warheads can generate quite believable energy signatures, holograms etc. of warships, which is used to lure at least some of incoming missiles away from really existing ships. There was a time when decoys used completely different system than missiles, but overtime both types of equipment grew into one. There rarely is a need to launch anything during last stage of an incoming missile salvo, and launching decoys too early means that enemy has time to figure out which of the target is a decoy and act accordingly. So you could as well simplify your ship construction by making it launch decoys through its missile launchers. The ability of decoys to pretend to be real warships and fool incoming attacks depends on many things, but it can be summed to technology and programming. During prolonged rocket duels the former is more important initially, but overtime the programmers on both sides reprogram their missiles prior to fire, making them smarter and smarter with every fired salvo. This forces the other side to improve their decoys, causing a little and massively sped up armaments race played on the battlefield. The exact number of missiles led astray varies between 15% and 50%, depending on both mentioned factors, making it one of the mos succesful types of defensive warheads.