Are you thinking of Air augmented rockets? Which capture and entrain surrounding air into their exhaust. https://en.wikipedia.org/wiki/Air-augmented_rocket htt

Are you thinking of Air augmented rockets? Which capture and entrain surrounding air into their exhaust. https://en.wikipedia.org/wiki/Air-augmented_rocket https://en.wikipedia.org/wiki/Air-augmented_rocket I have the impression that they see periodic use in various categories of mid-size military missiles.