The offensive began at noon on 30 March 1972, when an intense artillery barrage rained down on the northernmost ARVN outposts as the 56th and 57th Regiments were still in the process of occupying Camp Carroll and Strongpoint C-1. Two PAVN divisions (the 304th and 308th – approximately 30,000 troops) supported by more than 100 tanks (in 2 Regiments) then rolled over the DMZ to attack I Corps. The 308th Division and two independent regiments assaulted the "ring of steel", the arc of ARVN firebases just south of the DMZ.