Japanese Special Naval Landing Force departed Rabaul, New Britain aboard transports for the invasion of the RAAF seaplane base at Tulagi, Solomon Islands. On the same day, other transports at Rabaul embarked equipment necessary to build a new base at Port Moresby, Australian Papua. In Pearl Harbor, US Territory of Hawaii, Joseph Rochefort's cryptanalytic team intercepted a radio message from Isoroku Yamamoto to Shigeyoshi Inoue regarding Operation MO, in which Yamamoto made mention of northern Australia, thus giving Rochefort confidence regarding the hypothesis that Operation MO's target was Port Moresby.
