Beginning on March 2nd 1943 and lasting over the next two days, a battle was fought that determined the fate of the Japanese forces engaged against Allied armies on New Guinea. This battle was not fought between battleships. It was not a night surface action or a destroyer duel. The all-important aircraft carriers were not involved. No Wildcats, Corsairs, Dauntlesses, or Avengers did battle with the Japanese Kates, Vals, or Zeros. Yet it was such a complete victory for the Allied air forces in the area that the newly-developed and highly effective weapons and tactics used to defeat the Japanese were utilized by the Allies for the rest of the war.
The Battle of the Bismarck Sea pitted a Japanese convoy carrying urgently needed reinforcing troops and supplies from their bastion of Rabaul on New Britain to Lae on neighboring New Guinea against fighters and bombers of the US Army Air Corps (USAAC) and Royal Australian Air Force (RAAF). Except for a night attack by US Navy PT boats this battle was fought entirely by ships against land-based aircraft.
The Japanese had successfully landed troops and supplies at Lae before. Even though the Allies were able to decode Japanese radio traffic about a convoy planning to head from Rabaul to New Guinea in January, the attacking USAAC and RAAF aircraft were unable stop it. The convoy, consisting of five transports with five escorting destroyers, succeeded in landing most of their embarked troops and supplies even though the Japanese lost one transport (Nichiryu Maru) and had to beach another one (Myoko Maru) that was heavily damaged.
After a Japanese floatplane type often used for anti-submarine patrols in advance of convoys was sighted on February 7th 1943, General George Kenney (Allied Air Commander- Southwest Pacific) ordered increased aerial reconnaissance coverage of Rabaul believing something was cooking there. A week later there were 79 vessels in port, making it clear that another convoy, destination unknown but inferred, was forming up.
Once naval codebreakers were able to decrypt a coded message outlining the Japanese plans for the convoy the American and Australian commanders agreed to hit the convoy in the Vitiaz Strait between the islands of New Guinea and New Britain. This convoy would consist of eight military transport ships with eight escorting destroyers along with air cover consisting of about 100 Japanese fighter aircraft.
The Allied commanders agreed that the attacks on this convoy would need to be more effective than those used against the January convoy.
Hitting a maneuvering ship with a dropped bomb from any altitude is a dicey proposition at best. Up to that point 416 sorties had been flown against Japanese convoys in the New Guinea campaign resulting in only two ships sunk and three damaged. After conferring with experienced RAAF and USAAC pilots, the Allies decided to try bombing from different directions and altitudes simultaneously. Attacks by high altitude bombers would, it was hoped, disperse the convoy and allow more accurate bombing from medium altitude…and low altitude.
The USAAC had been modifying existing airframes with the intention of creating medium bombers General Kenney liked to call “commerce destroyers.” Kenney’s weaponeering genius, Major Paul “Pappy” Gunn, had stuffed four .50 caliber machine guns in the noses and extra fuel tanks in the bomb bays of some A-20 Havocs in late 1942. Thinking that the B-25 Mitchell bomber would also make an excellent “commerce destroyer”, Gunn tried the same thing with the B-25 but ran into some technical problems that he would later overcome.
Another innovative new tactic that would be attempted for the first time in the Pacific was skip bombing. The British and Germans had been using skip bombing for some time. When the RAAF demonstrated the basics of skip bombing and masthead bombing, both low-level attacks that attempted to put a bomb into the side of the target rather than through the deck, The USAAC pilots bought right in. Even a miss could heavily damage a ship if the bomb exploded under the ship (in all likelihood breaking her back) or over the ship (raking the decks with shrapnel and starting fires). The machine guns in the attacking bombers’ noses would cause serious damage to equipment and personnel on the ship even if the bombing attack was unsuccessful.
The Battle of the Bismarck Sea would be the Pacific debut of the gun-nosed strafing skip bomber.
The RAAF Beaufighters in the area were ready-made commerce destroyers in their own right. Equipped with four 20 millimeter cannons and six wing-mounted .303 caliber machine guns and capable of attacking with both bombs and torpedoes, the Beaufighter was one of the Allies’ best platforms for anti-shipping attacks.
The Allied order of battle shaped up with RAAF Hudsons, Beaufighters, Beauforts, and P-40 Kittyhawks of 71 and 73 Wings Royal Australian Air Force all tasked against the convoy. USAAC A-20 Havocs, B-25 Mitchells, B-17 Flying Fortresses, B-24 Liberators of the 38th, 43rd, and 90th Bombardment Groups, P-39 and P-400 Airacobras, P-40 Warhawks, and P-38 Lightnings of the 35th and 49th Fighter Groups, and the 3rd Attack Group made up the American forces. Totaling just shy of 200 aircraft, these combined Allied forces would have to contend with about 100 Japanese fighter aircraft tasked with covering the convoy.
Operating under the code name designation Operation 81, the convoy consisted of the Japanese destroyers Arashio, Asashio, Asagumo, Shikinami, Shirayuki, Tokitsukaze, Urinami, and Yukikaze, which carried a total of 958 troops bound for New Guinea. The Army transports Aiyo Maru (2,715 tons), Kembu Maru (950 tons), Kyokusei Maru (5,493 tons), Oigawa Maru (6,494 tons), Sin-ai Maru (3,792 tons), Taimei Maru (2,883 tons), Teiyo Maru (6,870 tons), and the Navy transport Nojima Maru (8,125 tons) carried the remaining 5,956 troops.
The Japanese ships departed Simpson Harbor on Rabaul on February 28th. The ships were able to take advantage of stormy conditions in the area until March 1st, when they were sighted by a searching B-24 Liberator. B-17s sent to the reported location failed to sight the convoy.
At dawn the next day, March 2nd 1943, another Liberator sighted the Japanese convoy. The first to attack were 28 B-17s. Attacking with 1,000 pound bombs from 5,000 feet, the B-17s sank the Kyokusei Maru and damaged Nojima Maru and Teiyo Maru. That evening 11 B-17s attacked the convoy again and damaged one more transport. RAAF PBY Catalina flying boats shadowed the convoy overnight.
The first Allied aircraft to take a shot at the Japanese convoy on the 3rd was a group of Bristol Beaufort torpedo bombers. The Beauforts were hampered by bad weather in the area and failed to score, but over 100 Allied attackers were forming up and preparing for their attack later that morning.
At 10:00 local time, 13 B-17s attacked the convoy from an altitude of 7,000 feet, which had the intended effect of dispersing the convoy. Then B-25s dropped their bombs from between 3,000 and 6,000 feet. These combined attacks caused a collision between two of the Japanese ships. As expected the B-17 and B-25 attacks didn’t run up the score, but they did draw Japanese anti-aircraft fire and leave the individual Japanese ships separated and ripe targets for the strafing masthead-level skip bombers.
13 RAAF Beaufighters roared in at masthead height disguising their attacks to appear to be torpedo attacks by Beauforts instead. The ships turned to face them in order to present as small a target as possible to a torpedo and paid a heavy price as the Beaufighters strafed the Japanese ships. Seven B-25s then attacked from 2500 feet while six more attacked from masthead height.
By the time 14 more B-25s finished their masthead strafing and skip bombing attacks that afternoon, a third of the Japanese transports were sunk or heavily damaged. American A-20 Havoc strafers then made their attacks using similar tactics and achieving similar results. B-17s bombing from high altitude claimed five more hits as well. The Allies kept pummeling the convoy for the remainder of the day using primarily USAAC B-25s and RAAF Havocs.
Navy Lieutenant Commander Barry Atkins led a force of 10 U.S. Navy PT boats out to attack the convoy on the night of March 3rd. Eight PT boats made attacks starting early in the morning of March 4th. The PT boats finished off one of the damaged transports but were unable to find additional targets for their torpedoes. Later that morning a B-17 sank the destroyer Asashio with a 500 pound bomb.
For the Japanese Army and Navy the battle was an unmitigated disaster. All eight cargo ships were sunk along with the destroyers Arashio, Asashio, Shirayuki, and Tokitsukaze. The destroyers Asagumo, Shikinami, Uranami, and Yukikaze were all damaged but lived to fight another day. Roughly 2900 Japanese sailors and soldiers were killed in the battle. Only about 1,200 of the nearly 7,000 troops who left Rabaul bound for Lae made it to New Guinea. Japanese destroyers and submarines pulled more than 2,700 survivors from the Bismarck Sea.
The Allies lost 10 aircrew in combat and another three in operational accidents, along with eight wounded. One B-17 and three P-38s were shot down. One Beaufighter and one B-25 were lost to operational accidents.
More indicative of the difficulties the Japanese encountered in their New Guinea campaign is their own postwar estimate that up to 20,000 troops were lost attempting to transit from Rabaul on neighboring New Britain across the Bismarck Sea to New Guinea. These losses were in large part due to Allied air power and the effective use of low-level strafing and skip bombing tactics. 35 percent of the bombs dropped from low altitude were hits. The Allies would use similar tactics with similar results against Japanese shipping for the rest of the war.