Around the middle of March 1944, Allied intelligence was monitoring reports about the movements of the 21st Wewak Resupply Convoy. Three subchasers were escorting three medium-sized merchant ships and a small “sea truck” from the Palau Islands for Wewak. The convoy’s position was accidentally betrayed by the Japanese, who did not know that the Allies had intercepted their communications, then detected by a couple of radar-equipped B-24s that had been sent to destroy the convoy before it reached Hollandia. The B-24s put one ship out of commission and the rest continued on to Wewak, reaching the base on the 18th, six days after leaving the Palau Islands.
With their location compromised, the Japanese worked through the night to quickly unload supplies and nearly 400 troops, then reload the ships with soldiers moving rearward to Hollandia early on the 19th. They hoped to avoid any further run-ins with Allied aircraft, as the convoy was carrying valuable cargo. In addition to the large number of passengers (1000), aboard one of the ships was a new radar system to detect enemy aircraft that was being moved to Hollandia, where the Japanese were building up their forces. At that time, the Japanese had very few of these radar systems.
B-24 crews from the 90th Bomb Group arrived at Wewak later that morning, only to find an empty harbor. They flew on, staying near the New Guinea coastline, and eventually found the convoy about 50 miles west-northwest of Wewak. Bombing the convoy from a medium altitude turned out to be mostly unsuccessful, although the crews may have sunk one of the escorts. Crews from the 22nd Bomb Group caught up to the convoy later that morning and were greeted by puffs of flack that stood between them and the convoy.
A three-plane element from the 19th Bomb Squadron attacked the Yakumo Maru, dropping 72 bombs around the ship, some of which landed within 50 feet of the ship. The 19th’s first attack was followed by an attack by the 33rd Bomb Squadron, then the 19th once again. Japanese fighters joined the fray in an attempt to defend the convoy below. During the chaos, the B-24s of 2/Lts. Ralph L. Anderson and G. Hill and 1/Lt. Chester G. Williams were holed by fighters. Hill’s plane suffered the most damage with a hit to the turbo-supercharger, damage to the outer left engine, the left wing and vertical stabilizer, as well as damage from a 20mm cannon shell to the fuselage.
After the fighters let up their attacks and the B-24s had dropped all their bombs, an explosion rocked the Yakumo Maru, which began listing dangerously. The two squadrons left the smoking convoy behind as they departed the area. Word of the convoy spread through Fifth Air Force and about 80 B-25s and A-20s converged on the convoy that afternoon. This time, the attacks on the convoy were completely uncoordinated. As an A-20 from the 3rd Bomb Group made its attack, it was accidentally shot down by an overexcited B-25. The 3rd also lost another A-20 after it hit the ship’s mast and had to ditch nearby. Both the pilot and gunner were rescued by a Catalina the following day.
In the end, the convoy was thoroughly destroyed, with only three members surviving the attack. As a result of the attack, the Japanese ceased sending convoys to reinforce the Japanese 18th Army, now trapped in northeastern New Guinea.