Battle of The Bismarck Sea - Aftermath

Aftermath

The battle was a disaster for the Japanese. Out of 6,900 troops who were badly needed in New Guinea, only about 1,200 made it to Lae. Another 2,700 were saved by destroyers and submarines and returned to Rabaul. About 2,890 Japanese soldiers and sailors were killed. The Allies lost 13 aircrew killed, of whom ten died in combat and three in an accident, and eight wounded. Aircraft losses were one B-17 and three P-38s in combat, and one B-25 and one Beaufighter in accidents. Due to miscounting of the Japanese force, MacArthur issued a communiqué on 7 March claiming that 22 ships, which included 12 transports, three cruisers and seven destroyers, had been sunk along with 12,792 troops. Army Air Force Headquarters in Washington, D.C. looked into the matter in mid-1943 and concluded that there were only 16 ships involved. However, GHQ SWPA elected to stick to its original story. After the war, Kenney would repeat the claim.

The Allied Air Forces had used 233,847 rounds of ammunition, and dropped 261 500 lb and 253 1,000 lb bombs. They claimed 19 hits and 42 near misses with the former, and 59 hits and 39 near misses from the latter. Of the 137 bombs dropped in low level attacks, 48, or 35%, were claimed to have hit, but only 29, or 7.5%, of the 387 bombs dropped from medium altitude. This compared favourably with efforts in August and September 1942 when only 3% of bombs dropped were claimed to have scored hits. It was noted that while the high altitude attacks scored few hits, they had dispersed the convoy, while the gunfire from the Beaufighters had knocked out many of the anti-aircraft defences. Aircraft attacking from multiple directions had confused and overwhelmed the Japanese defences, resulting in lower casualties and more accurate bombing. The results therefore vindicated not just the tactics of mast height attack, but of mounting coordinated attacks from multiple directions. The Japanese estimated that at least 29 bombs had hit a ship during the battle.

There was no doubt that the Japanese had suffered a major defeat. Imamura's chief of staff flew to Imperial General Headquarters to report on the disaster. It was decided that there would be no more attempts to land troops at Lae. The losses incurred in the Bismarck Sea caused grave concern for the security of Lae and Rabaul. This resulted in a change of strategy. On 25 March a joint Army-Navy Central Agreement on South West Area Operations gave operations in New Guinea priority over those in the Solomon Islands campaign. The XVIII Army was allocated additional shipping, ordnance and anti-aircraft units, which were sent to Wewak or Hansa Bay. Said Rabaul staff officer Masatake Okumiya of the defeat, "Our losses for this single battle were fantastic. Not during the entire savage fighting at Guadalcanal did we suffer a single comparable blow. We knew we could no longer run cargo ships or even fast destroyer transports to any front on the north coast of New Guinea, east of Wewak."

The planned movement of the 20th Division to Madang was revised in the light of what had occurred in the Bismarck Sea. The operation was postponed for two days, and the destination was altered from Madang to Hansa Bay further west. To reduce the Allied air threat, the Allied airfield at Wau was bombed on 9 March, and that at Dobodura on 11 March. Three Allied aircraft were destroyed on the ground, and one P-40 was lost in the air, but the Allied fighters claimed to have shot down nine Japanese planes. The transports reached Hansa Bay unscathed on 12 March, and the troops made their way down to Madang on foot or in barges. The 20th Division then became involved in an attempt to construct a road from Madang to Lae through the Ramu and Markham Valleys. It would toil on the road for the next few months, but its efforts would ultimately be frustrated by New Guinea's weather and the rugged terrain of the Finisterre Range.

Some submarines were made available for supply runs to Lae, but they did not have the required capacity to support the troops there by themselves. An operation was carried out on 29 March in which four destroyers successfully delivered 800 troops to Finschhafen, but the growing threat from Allied aircraft led to the development of routes along the coast of New Guinea from Madang to Finschhafen, and along both the north and south coasts of New Britain to Finschhafen, and thence to Lae using Army landing craft. It was by this means that the remainder of the 51st Division finally made the trip to Lae in May.

The necessity of delivering troops and supplies to the front in this manner caused immense difficulties for the Japanese in their attempts to stop further Allied advances. After the war, Japanese officers at Rabaul estimated that around 20,000 troops were lost in transit to New Guinea from Rabaul, a significant factor in Japan's ultimate defeat in the New Guinea campaign.

In April, Admiral Isoroku Yamamoto used the additional air resources allocated to Rabaul in Operation I-Go, an air offensive designed to redress the situation by destroying Allied ships and aircraft in New Guinea and the Solomon Islands. The operation was indecisive, and Yamamoto would himself become a casualty of Allied intelligence and air power.