It was May 1942, six months after hostilities had broken out. Thailand had declared war and permitted passage though her territory, adopting a helpful attitude, and to that extent she co-operated overall in the Japanese Army's transportation. Trains for military duties ran from Indonesia and Cambodia, and from Malaya, and movement of troops to Shōnan had become a comparatively harmonious practicality. The Thailand National Line's southern part gave on to the Bansoe junction in Bangkok, crossed Rama I bridge over the River Menam in the city and going South into the northern part of the Malay Peninsula reached Hat Yai. From the junction with Malayan Railways western line at Batam Bazaar on the frontier the line made possible unbroken transportation from Bangkok right into Singapore. Banpong station is about 80 km from Bangkok on this southern line. Construction of the railway began here. Its small station was the point of entry, and Japanese Army units on construction work and a labour force were moved into it, the labour force being prisoners-of-war to be employed as navvies and brought up from Malaya. Together with Nong Pladuk, 5 km east of Banpong, it became the construction base with huts, provision and fodder, a temporary ‘anchorage’ for groups passing through. Huts were built on the outskirts of the town in the Nong Pladuk direction. Materials were stockpiled meanwhile and the stockpiles grew taller and taller.

West of the town flowed the River Mae Khlaung which ran through about 50 km of the prefecture whose office was in Kanchanaburi town. From the front of Banpong station the highway to Kanchanaburi extended straight to the North. In front of the station was a small inn on the highway and in it 9 Railway Regiment's 1 Battalion (Sakamoto Unit), who had moved up from Sumatra, set up their HQ provisionally. On 20 May I reported to this HQ. Sakamoto Unit had been moved into Malaya at the outbreak of hostilities and had been restoring the captured Malayan Railways. Since March they had been running Sumatran railways. In May, on orders to prepare the construction of the Thai-Burma Railway, they had moved into Banpong as the regiment's advance party.