Saturation attack is a military tactic in which the attacking side hopes to gain an advantage by overwhelming the defending side's technological, physical and mental ability to respond effectively. During the Cold War and after, the conventional saturation missile attack against naval and land targets was and is a much feared eventuality.
Taking the design of an anti-ship missile as a theoretical example, one can begin with the goal of creating a missile which will get through and destroy its target 100% of the time. However, as a designer one knows that with time an opponent will develop counter measures that means that your missile will at some later date not be 100% effective. So given that a missile will only ever be less than perfect why not design a missile that will get through to the target say only 70% or even only 50% of time, with a cost saving benefit on each missile produced. Launched singly a missile with a 50% chance of getting through to its target will only get to its target 50% of the time, but with a salvo two such missiles the chance of at least one missile getting through is 75%, with three missiles 87.5% etc., with the probability that at least one missile will get through to its target becoming closer to certainty with each missile fired. If each missile has a warhead capable of destroying the target, then no individual missile can be ignored by the target warship and counter-measures. Thus, SAMs and CIW resources will have to be expended to defend the target. To further overload a target's ability to defend itself, an attacker can attempt to launch multiple missiles from multiple directions using different guidance options.
The main subscribers to the concept of the saturation missile attack were the Soviet Union and its client states. The Komar class missile boat for example being designed and operated around the calculations that it would take 12 P-15 Termit missiles to destroy a single NATO destroyer. At a time when British destroyers were equipped with just four anti-ship missiles, Soviet ships were going to sea with anything up to 20 anti-ship missiles, with even destroyers fielding 8 large missiles. With the NATO allies having followed the route of individually smaller and lighter missiles, NATO warships had the appearance of being underarmed when compared to Soviet ships with their multiple missiles in large container/launch tube housings.