Other difficulties were more directly associated with the nature of the sector rather than with its broad expanse. The positioning of the division in the west, although close to the coast, put the Marines beyond the range of protective naval gunfire. The sparse and inadequate road net further aggravated the tactical and logistical problems caused by wide separation of units. Finally, the cannoneers had exceptionally heavy demands placed on them due to the restricted amount of close air support allocated to frontline troops under operational procedures employed by Fifth Air Force. This command had jurisdiction over the entire Korean air defense system, including Marine squadrons. Manning the main line of resistance also frequently presented perplexing situations to the infantry. There had been little time for a thorough reconnaissance and selection of positions by any of the frontline regiments. When the 1st Marines moved into its assigned position on the MLR, the troops soon discovered many minefields, “some marked, some poorly marked, and some not marked at all.”[26] Uncharted mines caused the regiment to suffer “some casualties the first night of our move and more the second and third days.”[27] As it was to turn out, during the first weeks in the I Corps sector, mines of all types caused 50 percent of total Marine casualties. [26] Col Sidney S. Wade ltr to Deputy AsstCofS, G-3, HQMC, dtd 25 Aug 59. [27] _Ibid._ A heavy drain on the limited manpower of Marine infantry regiments defending JAMESTOWN was caused by the need to occupy an additional position, an outpost line of resistance (OPLR). This defensive line to the front of the Marine MLR provided additional security against the enemy, but decreased the strength of the regimental reserve battalion, which furnished the OPLR troops. The outposts manned by the Marines consisted of a series of strongpoints built largely around commanding terrain features that screened the 1st Marine Division area. The OPLR across the division front was, on the average, about 2,500 yards forward of the MLR. (See Map 3.) To the rear of the main line were two secondary defensive lines, WYOMING and KANSAS. Both had been established before the Marines arrived and both required considerable work, primarily construction of bunkers and weapons emplacements, to meet General Selden’s strict requirement for a strong defensive sector. Work in improving the lines, exercises in rapid battalion tactical deployment by helicopter, and actual manning of the lines were among the many tasks assigned to the division reserve regiment. [Illustration: MAP 3 K. White 1st MARINE DIVISION SECTOR 30 APRIL 1952] Rear and frontline units alike found that new regulations affected combat operations with the enemy in West Korea. These restrictions were a result of the truce talks that had taken place first at Kaesong and, later, at Panmunjom. In line with agreements reached in October 1951: