Japanese submarine operations against Australia in 1943 began when and I-21 sailed from Rabaul on 7 January to reconnoitre Allied forces around Nouméa and Sydney respectively.
As the Japanese force was too small to cut off all traffic between Australia and New Guinea, the Squadron commander widely dispersed his submarines between the Torres Strait and Wilson's Promontory with the goal of tying down as many Allied ships and aircraft as possible.