ing ▁North ▁Vietnam ' s ▁cap ability ▁to ▁in fil tr ate ▁and ▁send ▁men ▁into ▁South ▁Vietnam . ▁Again , ▁America ' s ▁shift ▁towards ▁inter diction ▁also ▁failed , ▁and ▁the ▁Johnson ▁administration ▁was ▁forced ▁to ▁change ▁the ▁priority ▁of ▁the ▁bomb ing ▁campaign . ▁For ▁the ▁third ▁phase ▁of ▁Rol ling ▁Th under , ▁which ▁occurred ▁from ▁spring ▁ 1 9 6 7 ▁to ▁early ▁ 1 9 6 8 , ▁bomb ing ▁operations ▁were ▁focused ▁on ▁industrial ▁and ▁transport ation ▁targets ▁in ▁and ▁around ▁H ano i , ▁H ai ▁Ph ong ▁and ▁the ▁buffer ▁zone ▁near ▁the ▁Chinese ▁border . ▁ ▁The ▁third ▁phase ▁of ▁the ▁campaign ▁was ▁heavily ▁fav ored ▁by ▁U . S . ▁command ers , ▁because ▁it ▁allowed ▁them ▁to ▁destroy ▁rather ▁than ▁just ▁threaten ▁H ano i ' s ▁nas cent ▁industrial ▁infrastr uct ures . ▁Furthermore , ▁the ▁new ▁targets ▁approved ▁by ▁the ▁Johnson ▁administration ▁enabled ▁U . S . ▁air power ▁to ▁be ▁used ▁against ▁the ▁primary ▁war - making ▁capabilities ▁of ▁North ▁Vietnam , ▁by ▁striking ▁at ▁military ▁targets ▁that ▁were ▁previously ▁denied ▁to ▁the ▁f ighter - b om bers ▁of ▁the ▁U . S . ▁Navy ▁and ▁Air ▁Force . ▁Thus , ▁in ▁ 1 9 6 7 ▁the ▁United ▁States ▁also ▁introduced ▁more ▁aircraft ▁into ▁the ▁operation ▁equ ipped ▁with ▁new ▁technology , ▁which ▁gave ▁American ▁air ▁units ▁the ▁assets ▁to ▁make ▁a ▁significant ▁difference . ▁However , ▁as ▁American ▁bom bers ▁moved ▁closer ▁to ▁H ano