Oeoso-ri having been an American housing area during the post-World War II occupation, duplex houses and Quonset huts were available. General Smith arrived by helicopter on the afternoon of the 19th, and the new CP opened at 1645. During the next few days the area was treated to intermittent artillery fire, apparently from a single well-hidden gun somewhere in the Seoul area. It was an embarrassment to Marine artillery officers, who were never able to locate the offending weapon, but no great harm was done. By this time General Smith could look forward to the arrival of more units at the front. On D-day the strength of X Corps on paper had been 69,450 ground force troops. In addition to the 1st Marine Division and 7th Infantry Division, there were such major units as the 93d and 96th Field Artillery Battalions, the 73d Tank Battalion, 56th Amphibian Tank and Tractor Battalion, the 2d Engineer Combat Group. In GHQ UNC Reserve were the 3d Infantry Division and the 187th Airborne RCT.[262] [262] GHQ UNC _OpnO No. 1_, 30 Aug 50. The 3d Division had not sailed for the Far East in time to take part in the Inchon-Seoul operation. The 187th Airborne RCT, due to land at Inchon on 23 September, had been the answer to General MacArthur’s requests in July for paratroops to land behind the enemy’s lines in conjunction with the amphibious assault planned as Operation BLUEHEARTS. Although the Joint Chiefs of Staff decided against flying an airborne RCT to Japan at the time, the 11th Airborne Division was later directed to organize and train such a unit for service in the Far East. On account of the large proportion of new troops filling out a skeleton unit, General Collins stipulated that the 187th was not to be committed for an airdrop before 29 September. It was decided, therefore, that the RCT would be given an initial mission of protecting the left flank of the 1st Marine Division. _Advance of RCT-1 to Sosa_ Preliminary planning for the crossing of the river Han began as soon as the Division staff settled down in the new CP. The reshuffling of various units had to wait, however, until both Marine regiments took their assigned objectives of 18 and 19 September. Throughout the 17th, while Murray’s regiment drove northeastward toward Kimpo, the 1st Marines had continued the attack from Ascom City along the Inchon-Seoul Highway. As mentioned previously, Monegan’s rocket launcher and the 75mm recoilless rifles, emplaced in 2/1’s positions on Hill 186, helped smash the North Korean tank-infantry column at dawn. It appeared that a second enemy force was supposed to have closed on Marine lines by taking a parallel course through the hills south of the highway. The Red infantry, in about company strength, was spotted moving along the high ground toward Company D’s front on Hill 186. Fox Company dispersed the column with mortar fire and then notified Dog to be on the alert.[263] [263] 2/1 _SAR_, 5; and Cunliffe interv, 24 Aug 54.