 On 3 January 1943 , Kenney received intelligence from Allied Ultra codebreakers that the Japanese were about to attempt a reinforcement run from their main base at Rabaul to Lae , on the mainland of New Guinea . He ordered Walker to carry out a full @-@ scale dawn attack on the harbor 's shipping before it could depart . Walker demurred . His bombers would have difficulty making their rendezvous if they had to leave Port Moresby in the dark . He recommended a noon attack instead . Kenney acknowledged Walker 's concerns but was insistent ; he preferred bombers out of formation to bombers shot down by the enemy fighters that were certain to intercept a daylight attack . In spite of this , Walker ordered that the attack be made at noon on 5 January . 
