Of course the radar in the US class D towers is used as a situational awareness tool as US class D controllers are not radar rated- just as in Australia.
About 50% of the 350 US class D towers have no radar coverage to the E airspace that adjoins the D.
In the USA the class D changes to E when the tower is not manned- not to class G as in Australia.
A very much safer system. Bring on NAS!