The flip flopping Japanese focus between New Guinea at the expense of Guadalcanal and then Guadalcanal at the expense of New Guinea was the single greatest air/land factor in the eventual Allied victory at Guadalcanal. With the Americans firmly established at the bottom of the Slot, the increased threat to their main base in the South Pacific at Rabaul convinced the Japanese that they needed to win New Guinea so they could focus back on the Americans in the Solomons.
The Japanese brought two divisions from China and Korea to reinforce the area. They established the next chain of island fortresses up the Solomon’s from Guadalcanal. They were to buy the time necessary so Imperial Japanese Headquarters could focus on stopping, and eventually rolling back, the American and Australian advances up the Kokoda Track in New Guinea.
On 2 March 1943, 7000 Japanese soldiers loaded onto nine transports, which would be escorted by eight destroyers. They were reinforce the troops facing MacArthur on New Guinea, and to land behind Allied lines near Kona, which would cut off the Allied advance. That area was chosen because it was the site of the first Japanese land defeat to the Australians the year before and they needed to erase that stigma of defeat.
Unfortunately for the Japanese, American and Australian code breakers knew of the plan and US BG Ennis Whitehead’s 5th Air Force was waiting. The heavy and medium bombers of the 5th Air Force had not been particularly effective against naval targets up to this point in the war. However,in the past six months, they made widespread organizational, tactical, and mechanical changes to their tactics and doctrine. Among many other changes, they put multiple heavy machine guns in the noses of the bombers, and perfected the tactic of “skipping” bombs into their targets like you would skip a stone across a pond. The changes proved very effective. On 3 and 4 March 1943, Whitehead’s air crews sank all of the transports and all but two of the destroyers in the Bismarck Sea between the islands of New Britain and New Guinea.
The Battle of the Bismarck Sea was the last time the Japanese would attempt to move large amounts of troops via sea transport without complete air superiority. Regrettably, the aftermath of the battle was ugly for both sides: Japanese machine gunned surviving American and Australian bomber crews and the Allies did the same to Japanese seaman and soldiers awaiting rescue in the sea. The Battle of the Bismarck Sea’s legacy became the arch-example of the dehumanizing ferocity that could characterize the War in the Pacific during WW II.