The first stage was a Thor missile in the DM-19 configuration. The second stage was the Delta, which had been derived from the earlier Able stage. An Altairsolid rocket motor was used as a third stage.
The Thor-Delta was the first rocket to use the combination of a Thor missile and a Delta upper stage. This configuration was reused for a large number of later rockets, and a derivative, the Delta II, remained in service into 2011.