The method chosen by PAVN to defeat the invasion was to first isolate the northern firebases by utilizing anti-aircraft artillery. The outposts would then be pounded by round-the-clock mortar, artillery and rocket fire. Although the ARVN firebases were themselves equipped with artillery, their guns were quickly outranged by PAVN's Soviet-supplied 122mm and 130mm pieces, which simply stood off and pounded the positions at will. The defensive edge that could have been provided by the utilization of B-52 bomber strikes was nullified by the close-in tactics of the PAVN. Massed ground attacks, supported by artillery and armor, would then finish the job.