This type of operational tactic--first to warn, then to carry out the threat--was not, however, the reason for the increased Chinese shelling. Rather, as it turned out, the enemy was about to embark on a series of limited objective attacks against the division flanks, starting first with major outposts guarding the most critical terrain on the MLR. The artillery and mortar fire of the 1st had been but an initial step. At 1830 on 2 October, Communist direct fire weapons opened up from an area 2,800 yards northwest of OP 36, lashing all the KMC outposts within range. A tank platoon, dispatched to counter the fire, returned at 1915 without having located the hostile emplacements. Shortly after the tanks returned, an extremely heavy artillery barrage again fell upon all of the KMC regimental outposts. Ten minutes later, seemingly on the signal of one red and one green flare, the enemy guns lifted their preparatory fires to permit an infantry attack. The ground action simultaneously struck OPs 37, 36, and 86, the forward positions closest to the Sachon River. At OP 37, the defending Korean Marine platoon fought valiantly for more than an hour against the assault of two enemy platoons, each of which required a company-size reinforcement before the Korean Marines were finally ousted. Although temporarily dislodged, they reorganized at the base of the position for a counterattack. Two counterattacks were made the next day, the second one carrying the Koreans to the top of the hill. Fierce enemy mortar and artillery shelling forced them to seek the shelter of the reverse slope before again renewing their assault. On 4–5 October, the outpost changed hands four times. At 1340 on the latter date, a heavy enemy artillery and ground attack compelled the KMCs to abandon their ravaged outpost; this withdrawal ended friendly control of OP 37 for the rest of the month. Nearby OP 36 was also lost. In the course of the night the Korean Marines on OP 36 turned back two Communist assaults, but fell under the weight of the third. By sunup on 3 October, the exhausted Korean Marines were forced to give ground; the Chinese immediately occupied OP 36 and held it. One more KMC outpost was to fall during the first week. OP 86 guarded the southwestern two-thirds of the regimental sector and frequently was the target of artillery shelling and ground attacks. This position was also the most distant from the main line and the closest to the Sachon River.