In order to transport prisoners, the ship was fitted out with extra decks constructed of bamboo subdivided into cages of the same material. Deck space was also used for the prisoners. When she was attacked and sunk on September 18, 1944, by HMS Tradewind, Junyō Maru was packed with 1,377 Dutch, 64 British and Australian, and 8 American[3] prisoners of war along with 4,200 Javanese slave labourers (Romushas) bound for work on the railway line being built between Pakan Baru and Muaro in Sumatra. It was the world's greatest sea disaster at the time with 5,620 dead.[4] 680 survivors were rescued, only to be put to work in conditions similar to those of the Burma Railway where death was commonplace.[2]