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.