Captured documents indicated that enemy forces in unknown numbers had already infiltrated through gaps in the eastern sectors of the Eighth Army’s Line D. Guerrilla activity was reported as far west as Tanyang, on the MSR of IX Corps, and as far south as Taejon, threatening the supply line of I Corps. Train ambushes occurred on 13 January in the Namchang area and to the south of Wonju. Other attacks took place on the rail line about 60 miles north of Taegu. In expectation of further attempts, trains were provided with a sandbagged car, pushed ahead of the engine, to absorb the shock of landmine explosions. Another car was occupied by guards who had the duty of dealing with direct guerrilla attacks.[50] [50] EUSAK _Cmd Rpt_, Jan 51. The tactical problem of the Marines was quite simple--on paper. About 1,600 square miles, most of them standing on end in mountainous terrain, were included in the new zone of operations. The experience of World War II had demonstrated how effective guerrilla warfare could be as an adjunct to large-scale military operations. Officers of the 1st Marine Division had no illusions about their mission, therefore, when they received unconfirmed reports of NKPA guerrilla infiltrations behind the EUSAK lines toward Andong. All uncertainty vanished on 18 January, shortly after the issuing of OpnO 3-51, when a patrol of the 3d Battalion, 1st Marines, flushed out an undetermined number of North Korean troops east of Andong. They took to their heels so earnestly that the Marines barely managed to catch three of them after a long chase. The prisoners identified their unit as the 27th Infantry of the NKPA 10th Infantry Division. The other two regiments, the 25th and 29th, were also in the general area. All three were supported more in theory than fact by artillery, mortar, medical, and engineer units organic to the division. In reality, however, the estimated total of 6,000 troops consisted largely of infantry, A few mortars, according to the prisoners, were the largest weapons. Following the Inchon-Seoul operation, the remnants of the badly mauled NKPA 10th Infantry Division had straggled back across the 38th Parallel to the Hwachon area. There they were reorganized by the Chinese for guerrilla operations and placed under the command of NKPA Major General Lee Ban Nam.[51] [51] 1stMarDiv Periodic Intelligence Report (_PIR_) 87–94, 17–22 Jan 51.