In the Spring of 1942, with a pause after the occupation of Singapore, the campaign to occupy Burma went ahead. As Rangoon was the supply-base for Burma, for Southern Region Army GHQ there arose the urgent problem of the safety of the supply route by sea. In Burma the British-Indian Allied Forces had given in to the Japanese Army's offensive in a crushing defeat, but because of submarines from the British Western Fleet operating in the Andaman Sea off Burma the Japanese maritime supply-route was threatened, so the overland part of the preparations for the campaign to recapture Burma on the way to India was pressed forward. This year in June in the battle off Midway Island the Japanese Navy lost from its main force four aircraft-carriers sunk, a heavy blow which destroyed the hope of any defence in the Andaman Sea. The safety of transports out of Singapore to seas off Burma had become a problem. Southern Region Army used the plan for an overland route to Burma, taking advantage of the study made in 1939 at Daihonéi (Imperial Japanese Army HQ in Tokyo) to find what use could be made of a railway out of Thailand into Burma. In their survey, construction of a railway would need ‘two railway regiments taking about a year’. Major-General Hattori Shimpei, commanding Southern Region Army's 2 Railway Control, resolved in February this year to make a survey on the ground of this railway project. On receipt of his order, Staff Officer Irie, together with Railway Official Nishijima surveyed the area from Kanchanaburi up to the Three Pagodas Pass on the frontier. They judged that the volume of work needed was much greater than in the original estimate, and calculated that it would take over two years. It therefore became urgent for the construction to start promptly, so without waiting for Daihonéi's orders the General assigned in March 1942 the main construction units, namely 1 Railway Materials Workshops, 5 Railway Regiment, and 9 Railway Regiment.