During World War II, when Australia was among the nations at war with the Axis powers, the Japanese invaded the nation with only a small reconnaissance party in the Kimberley on 19 January 1944; they were investigating reports that the Allies were building large bases in the region. Four Japanese officers were on board a small fishing boat. They investigated the York Sound region for a day and a night before returning to Kupang in Timor on 20 January. After returning to Japan in February, the junior officer, who had commanded the party, suggested using 200 Japanese prison inmates to launch a guerrilla campaign in Australia. No superior adopted his suggestion, and the officer was posted to other duties.