In January 1944, "Mainline" Japanese Army codes were broken with help from a buried trunk found during the Battle of Sio in New Guinea by Australian troops of the 9th Division. The records had been left by retreating Japanese Army troops of the 20th Division (Tokyo was told the papers had been burnt, but the lieutenant did not want to reveal his position by burning them), so they were buried in a metal strongbox near a stream. They included the army codebook "Rikugun Angosho Number Four" (which was fed into Sinkov's IBM machines); two additive books and codes for these traffic identifiers (which were now readable): 2345, 5555, 6666, 7777 and 7870; and an instruction book on how to use the other books. The Central Bureau spent a day drying the damp pages, and the flood of decoded messages that ensued meant that MacArthur had to ask the US Navy for assistance. Two translators, Forrest Biard and Thomas Mackie were sent from FRUMEL.