Operation Killer Operation Killer was the start of the second major counter offensive launched by United Nations forces against the People ' s Volunteer Army and the North Korean Army during the Korean War between 20 February and 6 March 1951 . The offensive was formulated by General Matthew Ridgway with the goal of annihilating enemy forces below the Arizona Line and was immediately followed by Operation Ripper . Battle . The 2nd Division jumped - off on " Operation Killer " on 22 February . The initial advance was slow , not so much due to resistance as to terrain . The sector assigned to the 2nd Division presented enormous problems . However , by 1700 hours both the 9th and 38th Infantry Regiments had reached the Chuchon River where swift waters and a lack of bridges delayed crossing . The engineers constructed a foot bridge for immediate use of the 9th Infantry and , in the 23rd Infantry Regiment ' s zone of advance , tanks of the regimental tank company were used to ferry people to the north bank . The 9th Infantry ran into moderate resistance on 23 February but with all three battalions teaming up , an enemy force of 2 , 000 was routed , dispersed to the north , leaving their dead and wounded behind . The Second Battalion of the 23rd Infantry , with the 37th Infantry FA Bn attached , moved east into the 7th Division zone on 26 February in preparation for an attack on the following day on Ungyo - ri , an important town on the Hoengsong - Pangnimni road . The 9th Infantry , after securing Haanhung - ni , west of Ungyo - ri , sent a battalion eastward along the road in anticipation of an enemy withdrawal from Ungyo - ri when the Second Battalion of the 23rd Infantry launched its assault . The evening of this last day of February found the 2nd Division in positions astride the Hoengsong - Pangnimni road in its sector and preparing to continue its advance to Phase Line Arizona which paralleled the road roughly 7 , 000 meters to the north . Ahead of the Division were strong elements of the 17th and 18th CCF Divisions and lesser elements of the III and V North Korean Corps which were retreating slowly to the north in the face of the grinding X Corps offensive . Intelligence reports indicated the foe intended to delay the advance as much as possible while he prepared fixed defenses north of the 38th parallel . " Operation Ripper , " was designed to carry UN forces to the 38th Parallel . Similar to " Operation Killer " it aimed at maximum destruction of enemy personnel and equipment with minimal friendly casualties . It wasn ' t the character of the opposition so much , although at times throughout the month it was fanatic and as strong as any ever faced . It was the terrain , coupled with alternate spring thaws , rains and days of sub - zero freezes which hampered every activity and wrought unprecedented burdens on every unit and operation . The operation concluded by the end of March . Aftermath . Over the fourteen days the two corps took to reach and consolidate positions along line Arizona , each reported having inflicted substantial enemy casualties . The IX Corps alone reported 7 , 819 enemy killed , 1 , 469 wounded , and 208 captured . But from the outset it had become steadily clearer that the primary objective of Operation Killer of destroying all enemy forces below the Arizona line would be only partially achieved . The enemy forces ' head start in withdrawing , their disinclination to take a defensive stand below the objective line other than in spotty delaying actions , and Eighth Army difficulties in negotiating the ground had prevented any other result .