Smoke screens are obviously not going to be useful as defenses for things like missiles, since the smoke immediately slows down when it collides with the air wh

Smoke screens are obviously not going to be useful as defenses for things like missiles, since the smoke immediately slows down when it collides with the air while the missile/projectile continues on at high speed. (It might be useful in space, where you'd be creating something like a comet's halo, which separates from the body on a much longer timescale.)