Japanese conquest of Burma main attack westward from Rahaeng in Thailand across the Kawkareik Pass. The 16th Indian Infantry Brigade of the 17th Indian Division guarding this approach retreated hastily westward. The Japanese division advanced to Moulmein at the mouth of the Salween River which was garrisoned by the 2nd Burma Infantry Brigade. The position was almost impossible to defend, and had the River Salween, almost wide, behind it. The 2nd Burma Brigade was squeezed into a progressively tighter perimeter, and eventually retreated over the river by ferry on 31 January after abandoning a large amount of supplies and equipment. Part of the force
Burma Railway and 250,000 Southeast Asian civilian labourers ("rōmusha") and about 61,000 Allied prisoners of war were subjected to forced labour during its construction. About 90,000 civilian labourers and more than 12,000 Allied prisoners died. A railway route between Burma and Thailand, crossing Three Pagodas Pass and following the valley of the Kwhae Noi river in Thailand, had been surveyed by the British government of Burma as early as 1885, but the proposed course of the line – through hilly jungle terrain divided by many rivers – was considered too difficult to undertake. In early 1942, Japanese forces invaded Burma and seized