Anti-ballistic missile defense countermeasures are tactical or strategic actions taken by an attacker to overwhelm, destroy, or evade anti-ballistic missile defenses.
Finally, they can be categorized by which part of a ballistic missile's flight they are active (boost, bus, midcourse, or terminal phases).
The simplest countermeasure to an ABM defense is to simply increase the size of the attack.
This can be done by adding more ICBMs, by increasing the number of warheads delivered by each ICBM using MIRVs, by using SLBMs (which have a much shorter flight time and are thus difficult to destroy before the terminal phase), or by a heavier reliance on bombers and cruise missiles.
These countermeasures include using fast-burn boosters (which limit the time allowed for boost-phase intercept), light-weight ICBM skirts which limit the infrared signature of the booster (rocketry), use of decoys (e.g., lightweight mylar balloons which, until re-entry, will travel on an identical trajectory with the heavier warheads), use of Ablation materials or reflective coatings which limit the damage of directed energy weapons, launches of numerous harmless missiles early in an attack which might cause the defender reveal their defenses and expend valuable resources.