[Merad]

Japan has Patriot systems and several Aegis equipped ships, and both of those have ABM capability. Ballistic missiles are just much harder to shoot down than normal surface to surface or air launched missiles, especially when you’re using SAM’s like Patriot that are relatively short range. I think there just isn’t a very high confidence level in ABM systems. Even the US’ dedicated ABM system, which consists of long range missiles based in CA and AK, is expected to need four shots to achieve a 97% probability of kill (the system only has 44 missiles).

The US had a test platform [0] that showed that the concept of an airborne laser ABM system was viable. However they concluded that we need an order of magnitude increase in the power of airborne lasers in order for it to have enough range to actually be useful.

0: https://en.wikipedia.org/wiki/Boeing_YAL-1