Division OpnO 27-51 designated the 1st Marines to relieve the ROKs on Hill 854 and complete the seizure of that terrain feature, if necessary. As a preliminary, the 1st Battalion of the 5th Marines (Lieutenant Colonel William P. Alston) took over the front of the 1st Marines on the HAYS line. This enabled 1/1 and 3/1 to enlarge the Division sector by side-slipping to the east while Lieutenant Colonel Franklin B. Nihart’s 2/1 went into immediate reserve just behind the main line of resistance.[303] [303] The balance of this section is based on the 1stMarDiv _HD_, Sep 51, 18–24, and on 1/1 and 3/1 _HD_, Sep 51. The 1st Battalion of the 1st Marines (Lieutenant Colonel John E. Gorman) relieved two battalions of the 10th ROK Regiment in the Hill 854 area. No opposition from the enemy was encountered, but the Marines suffered 11 casualties from mines as a consequence of incorrect charts supplied by the ROKs. [Illustration: 1st MARINE DIVISION ZONE OF ACTION SITUATION ON 20 SEPT 51 MAP 20] By this time it had become an open question whether “friendly” mines did more harm to friend or foe. Certain it was, at any rate, that the prevailing system--or lack of system--resulted in Marine casualties during nearly every offensive operation in zones where the action shifted back and forth. Lieutenant Colonel Foster C. La Hue’s 3/1 relieved two battalions of the 21st ROK Regiment. Although the ROKs had fought their way to the summit of Hill 854, the ridgeline to the southwest remained in the enemy’s hands. An attack by 3/1 was planned for 1530 on 20 September, supported by artillery and an air strike. Delays in the arrival of the planes caused a postponement until 1720. How Company jumped off and had advanced 50 yards when a man was killed and another wounded by mines. The attack was called off at dusk so that the ROKs could remove the explosives they had planted. Air support was requested for 0700 on the morning of the 21st, but it was 1040 before four Air Force F-51s arrived for a strike directed by an observation plane of VMO-6 and a forward air controller. At 1220, following a 10-minute artillery preparation, How Company spearpointed a battalion attack which met stiff resistance. Another air strike was requested but did not materialize. The assault continued with mortar and artillery support until 1745, when How Company reported the ridge line secured. Casualties of 3/1 for the two days were nine KIA and 55 WIA. Enemy losses totaled 159 counted and 150 estimated KIA, 225 estimated WIA, and 29 prisoners.[304] [304] Sources for the action on Hill 854 are the 1/1 and 3/1 historical diaries for September 1951. “A large number of mines and booby traps were discovered within the battalion sector,” the 3/1 report for the 23d concluded, “most of these being U.S. types which were placed by ROK troops, with only a few enemy mines scattered in the central portion of the sector.”[305] [305] 3/1 _HD_, Sep 51, 8.