ICBMs require significant infrastructure, for storage, fueling, and launch. Once in the air, their targets are known quickly and intercepts are difficult but p

ICBMs require significant infrastructure, for storage, fueling, and launch. Once in the air, their targets are known quickly and intercepts are difficult but possible. (Airspeed is their only defense.) Cruise missiles require much less pre-launch facilities, and once in the air, fly very low altitude trajectories, at speeds similar to aircraft. Small size, GPS steerable trajectories, low altitude all make them very hard to detect. Defense of fixed targets would require large radius flat clear areas with radar controlled AA guns (think Phalanx etc). Nuclear propulsion means extreme range / flight time and multiplies the threat profile per missile in inventory.