The Japanese were well-established on the northern coast of New Guinea and had begun a summer offensive in 1942 to drive across the mountains and take Port Moresby on the southern coast. Major General George C. Kenney, MacArthur's top air commander, organized the Fifth Air Force in September 1942, and gave it a single immediate mission: seize and hold air superiority over New Guinea.

Hitting the enemy bases at Buna and Lae, Douglas A-20 light bombers roared in a few feet above the water, dropping a new weapon: the parafrag bomb. It was a 23-lb. fragmentation bomb with a rudimentary parachute attached, and an instantaneous fuze. It dropped nose first, hit, and exploded in a steely scythe that sliced into Japanese aircraft.

It was one of several innovative field adaptations of existing weapons by Fifth AF. A-20s were modified to carry four 50-caliber machine guns in their noses for strafing. The B-25s were altered to carry eight of the same weapons. Thus armed, a light or medium bomber could attack airfields or shipping, the two major targets for Fifth AF, drop its bombs, and swing back to strafe.

On 1 March 1943, Kenney's airmen, augmented by Royal Australian Air Force pilots flying Bristol Beaufighters, caught a 16-ship Japanese convoy in the Bismarck Sea. For three days, bombers and fighters of the Fifth and the RAAF worked over the vessels. Only four escorting destroyers managed to get away. Hundreds of survivors were left clinging to rafts and floating debris. On the fourth day, the planes came back and ruthlessly hunted down and strafed the hapless Japanese troops. It was the end of attempts to supply Lae by organized convoys.

In October, the Fifth hit Rabaul, giving Admiral William Halsey an assist with his assault on Bougainville. Navy and Thirteenth AF planes pitched in, and together they destroyed enemy air power in New Britain. Early in 1944, a sustained air offensive knocked Rabaul out of action, and the Fifth turned its attention to Hollandia. A three-day attack, starting on 1 April 1944, devastated the place.

Pre-invasion strikes against the Philippines began in August 1944, with attacks on Mindanao Island, but MacArthur decided to go directly for Leyte. Fifth AF destroyed 314 Japanese planes in that campaign for a loss of 16 of their own. Luzon Island was next.