As an added complication, it was necessary to build up a 10-day reserve of ammunition at ASP 60-B so that Division transport would be available for lifting 2,000 rotated troops to Chunchon some time between 3 and 15 September. This meant that 50 to 60 Marine trucks must be employed daily to haul ammunition, with the result of a drastic shortage of motor transport for other purposes. Only human transport was available for supplying Marines on the firing line. X Corps started the month of September with 20,070 Korean Service Corps, the successor to CTC, and civilian contract laborers--the equivalent in numbers of a U.S. Army infantry division. Even so, 14 air drops were necessary during the month, only one of which went to a Marine unit. This took place on 1 September, when 20 Air Force cargo planes from Japan dropped ammunition and rations to the KMCs. A 90 percent recovery was reported.[274] [274] X Corps _Cmd Rpt_, Sep 51, 41–42; 1stMarDiv _HD_, Sep 51, 5–6. It generally took a full day in the 1st Marine Division zone during the first week of September for a cargador to complete the trip from a battalion supply point to the front lines and return. This made it necessary to assign from 150 to 250 Korean laborers to each infantry battalion. And as the Marines advanced farther into the rugged Korean highlands, the logistic problem was increased. _Resumption of Division Attack_ Enemy groups moving southward into the zone of the 1st Marine Division during the six-day lull were sighted by air observation. POW interrogations and other G-2 sources established that the 2d NKPA Division, II Corps, had been relieved by the 1st NKPA Division, III Corps. Accurate 76mm fire from well-hidden guns was received by the Marines throughout the interlude, and patrols ran into brisk mortar fire when they approached too near to enemy bunkers on Hill 673. For the second time, during the night of 4–5 September, 5th Marines units were assailed on the KANSAS Line, 5 miles to the rear of the 7th Marines troops similarly deployed along the HAYS Line. Yet a large 7th Marines patrol ranged forward some 2,000 yards the next day without enemy contacts. A like result was reported by a patrol representing almost the entire strength of the Division Reconnaissance Company (Major Robert L. Autry) after it scoured the area north of the Punchbowl.[275] [275] This section, except when otherwise specified, is based on the following sources: EUSAK _Cmd Rpt_, Sep 51, 38–53; X Corps _Cmd Rpt_, Sep 51, 9–12; 1stMarDiv _HD_, Sep 51, 8–14; 7th Mar _HD_, Sep 51; 1st, 2d, and 3d Bns of 7th Mar, _HD_s for Sep 51. 1st Marine Division OpnO 23-51, issued on the morning of 9 September, called for the 7th Marines to jump off at 0300 on the 11th and attack Objectives ABLE and BAKER--Hills 673 and 749 respectively--white maintaining contact with the 8th ROK Division on the right. Other Division units were given these missions: