It is April, 1943. A year ago, the Japanese stood proud and victorious in the Pacific, having beaten
their enemies at Malaya, the Philippines, the Dutch East Indies, Burma and at pretty much every
place they had attempted to invade. But today, the tide has turned completely in favor of the Allies,
who had successfully checked them at Midway and the Kokoda Track, culminating with triumphant
counter-offensives to retake Guadalcanal and the Buna-Gona area. Now, with the subsequent
capture of the Russell Islands and the disastrous Battle of the Bismarck Sea, all signs pointed
to a continuous Allied offensive that would not stop until the Empire was brought to its knees.
Admiral Yamamoto, mastermind of the Pearl Harbor attack and commander-in-chief of the Combined
Fleet, knew that Japan needed some time to prepare a new set of defenses if the Empire hoped
to survive . Thus, he would set forth to launch a massive air offensive against the Allied positions
in the South Pacific. Join us as we delve into Yamamoto’s last offensive: Operation I-Go.
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As we last saw, the situation had changed drastically for the Japanese Empire in the
Pacific War. While the Allies planned to undertake the next phase of offensives against Japan in
what would be known as Operation Cartwheel, the Japanese were also shifting their priorities to
the successful defense of New Guinea, particularly the key Lae-Salamaua area. This is why Admiral
Yamamoto and the Combined Fleet staff were greatly incensed by the disaster that transpired in the
Bismarck Sea, as the Japanese convoy was meant to reinforce Lae. They were also concerned about the
state of land-based aviation, which had failed to protect the convoy during the battle, recognizing
that Admiral Kusaka’s 11th Air Fleet had suffered many losses in the last few months, including
most of its original aircrews. Furthermore, the remaining air groups also suffered from a series
of serious issues, but there were two that were most important: the poor health and low morale
that Rabaul was experiencing due to widespread diseases, including malaria and chronic diarrhea;
and the poor quality of replacements for the original veterans, many of them unfamiliarized
with the aircraft employed in Kusaka’s command and requiring to be trained again after their arrival.
The accelerated flow of replacement aircrews to the frontlines was actually a fleet-wide trend,
as the IJN shortened the training syllabus for commissioned and enlisted pilots by two months.
To achieve this reduction, the amount of instructional time devoted to skill areas such as
gunnery, tactics, and formation flying was reduced or in some cases eliminated. Surviving pilots that
had started the war in the third position of a three-plane sector even rose to the role
of shotai or chutai leaders without having the experience to really assume such responsibilities.
Thus, the March 25 directive to establish a “superior and impregnable strategic position”
finally put an end to the great Southern Offensive, as Tokyo implored Army and Navy
to operate as one unit in the defense of their precious gains, while at the same time maintaining
pressure on Allied forces in New Guinea. To implement this new directive, General Imamura
decided to summon a conference on Rabaul on April 12, attended by the commanders of the 17th and
18th Armies, the 6th Air Division, and units under direct Army Area command. At this conference,
it would be decided that General Hyakutake’s 17th Army was to assume responsibility for the defense
of the northern Solomons in coordination with the Navy, with the additional mission of assisting
them during the incoming attacks on the central Solomons; while General Adachi’s 18th Army was to
secure a firm strategic position at Lae-Salamaua via the establishment of overland and coastal
supply routes linking Madang and western New Britain with the Lae area. The construction
of naval and air bases in the eastern New Guinean coast was also to be sped up so that the 6th Air
Division of Lieutenant-General Itahana Giichi could gradually advance its bases of operations
there. Though a step in the right direction for the Japanese, these orders would be difficult
to accomplish, as American aircraft had already made destroyer runs to Finschhafen impossible,
further wearing down the strength of the Japanese units in New Guinea with constant air attacks.
Therefore, the only means of moving men and supplies to Lae would be through slow and arduous
transport by submarine and small craft, and the debilitated forces already stationed there would
be unable to take any offensive action. But there was also a small offensive element in the March 25
plan, directing the IJN to start an air campaign against Allied positions in the Solomons and New
Guinea. Knowing that the 11th Air Fleet by itself was incapable of mounting an effective strike,
Admiral Yamamoto called upon the 3rd Fleet, now under the command of Admiral Ozawa , to
contribute its carrier air groups to the effort. Thus, the carriers Zuikaku, Zuiho, Junyo and Hiyo
would contribute over 160 aircraft to the 155 already under the command of Admiral Kusaka,
for an estimated total of 350 aircraft. After initially concentrating in Rabaul,
these planes were dispersed to several airfields on Bougainville and the
Shortlands for Operation I-Go, the massive air counteroffensive scheduled to start on April 5.
In the meantime, Kusaka decided to send a preliminary fighter sweep down the Slot on
April 1, hoping to draw out and destroy a large percentage of the Allied fighters at Guadalcanal.
After launching 54 Zeros in two separate waves , the Japanese raiders would be intercepted by 42
fighters from Admiral Mason’s ComAirSols command over the Russell Islands, starting a giant melee
that lasted nearly three hours . Fighting over their own territory, the Americans would shoot
down nine Zeros at the cost of five Wildcats and a Corsair. This was not a promising start for the
Japanese, but inflated reports would nonetheless leave them satisfied about this first attack.
On April 3, Yamamoto and his staff would finally arrive at Rabaul, as he was to personally take
command of the operation alongside Admirals Kusaka and Ozawa . Although the air counteroffensive
was to start on April 5 with Attack X, the planned strike against Guadalcanal,
bad weather would finally force the Japanese to postpone it for two days. The Japanese
would find no shortage of tempting targets on Guadalcanal, or in the surrounding anchorages.
During the few short weeks since they had conceded the island, the Americans had completed its third
airstrip and Guadalcanal had become a supply depot with massive dumps of munitions, fuel and
weapons dumps. Japanese reconnaissance flights on March 25 further revealed approximately 300
Allied planes on the island, and the snoopers counted numerous transports, cargo ships,
and warships riding at anchor between Lunga Point and Tulagi. In the early hours of April 7, Attack
X would finally be launched under the personal supervision of Yamamoto, as a massive strike force
of 110 Zeros and 67 D3A dive bombers lifted off en route to Guadalcanal, shortly stopping at the
Shortlands to refuel. Additionally, a separate group of 47 Zeros from the 11th Air Fleet took
off from Buka and also headed southeast, for a grand total of 224 planes, the largest Japanese
striking force since Pearl Harbor. Yet the Allies enjoyed an experienced and talented intelligence
network at this point in the war, so they would receive several warnings of the impending attack.
It’s worth highlighting the remarkable work of Australian coastwatchers, which had been
transmitting reports of their visual sightings ever since the start of the Pacific War.
Consequently, Rear-Admiral Marc Mitshcer, the new commander of AirSols, began to scramble
76 fighters from Henderson Field and the outlying airstrips, though in great disorder.
And despite the early detection, the Japanese also bought extra time by cleverly splitting the attack
force into four groups, which created initial confusion among the Allied radar controllers.
As the four squadrons of Vals were preceded by two sweeps of fighters,
three squadrons of Wildcats would get to intercept them, rapidly engaging in an air duel.
Yet despite their best efforts , they would be unable to prevent the Vals from attacking targets
in Tulagi anchorage. As a result, three ships would be sunk: the veteran American destroyer
Aaron Ward, the small New Zealander corvette Moa and the US tanker Kanawha of 14500 tons.
Luckily, the Americans were able to evacuate their bombers from Henderson Field before it
got attacked, so not much damage would be scored against Guadalcanal. After the fight broke up,
most of the surviving Vals and Zeros would head back towards Bougainville, though some would have
to ditch or land at Munda. Japanese losses in this engagement totaled 12 Zeros and 12 Vals, including
that of future writer Toyoda Minoru, who would be later rescued and imprisoned by the Americans.
In turn, the Japanese aviators claimed 41 American planes destroyed, although only
seven Wildcats were lost, and the dive bomber crews claimed to have sunk 12 major vessels;
so Yamamoto and his staff were very pleased by the outcome of this strike.
Because of this apparent success, Yamamoto would proceed to approve Attack Operation Y,
a series of air raids against bases in New Guinea. The first would be carried out on April 11,
as 73 Zeros and 27 carrier dive bombers departed Rabaul and attacked Oro Bay, adjacent to the
rapidly expanding airdrome complex at Dobodura. A total of 50 Allied fighters scrambled from
Dobodura and intercepted the force, shooting down two Zeros and four Vals without loss. Despite the
number of Japanese aircraft involved, the results were surprisingly modest: only one American cargo
vessel sunk, a transport heavily damaged and an Australian minesweeper damaged. Early the next
morning, Yamamoto traveled to Vunakanau airdrome to personally send off another strike, this time
against Port Moresby. An inspiring sight in his crisp white uniform, he waved to the passing crews
as 43 G4M medium bombers lifted off, shortly followed by an escort of 65 Zeros. A separate
fighter sweep of 66 Zeros was also assigned to the raid, for a grand total of 174 aircraft.
Flying in two large formations, the Japanese initially headed towards Milne Bay, which allowed
the Americans to detect them with a radar station. Consequently, General Kenney would scramble every
operational fighter on the near side of the Owen Stanleys. Yet the initial approach to Milne was a
feint, and soon, a different warning would report them crossing the mountain range. This gave the
attackers an ideal opportunity to cause serious harm, and although they would be intercepted by
44 Allied fighters, the Japanese bombers would be able to penetrate the defensive fighter screen.
Failing again to take advantage of their numerical superiority, the two Japanese
formations separately attacked outlying fields instead of concentrating on one important
target . Nonetheless, the attackers would blanket the airstrips and crater the runways with bombs,
successfully damaging numerous ground installations and some 15 aircraft, as
well as destroying three B-25s and a Beaufighter on the ground. The Japanese also claimed the
sinking of a transport anchored in the harbor and the destruction of 28 enemy planes, although
only two P-39s would be shot down. In contrast, the Japanese lost two Zeros and seven Bettys.
On April 14, as the Japanese air offensive was nearing its conclusion, Yamamoto would yet again
send off the next attack in person, this time against Milne Bay. With a combined strength of
196 aircraft , including 75 Zeros and 23 Vals from the carriers Hiyo and Junyo that were joined by
54 fighters and 44 Bettys from Admiral Kusaka’s 11th Air Fleet, the Japanese set out to deliver
a deadly blow against the Allied forces. Although Milne Bay enjoyed a low cloud base for most of
the year, with the nearby mountains making flying in this area a dangerous proposition,
the attackers had gotten lucky when they chose their last objective, as the Allies had rerouted
most of their shipping to Milne Bay due to the recent raid on Port Moresby. Fortunately,
the Allies would receive advance warning of the attack, so the Australian harbor master,
Commander Geoffrey Branson, would order the vessels to disperse while General Kenney scrambled
some 44 fighters to intercept the enemy strike. Yet despite the best efforts of the Allied airmen,
the Japanese would once again get through, with its bombers attacking Milne Bay in several waves.
Initially, high level bombers dropped at least 100 bombs on the anchorage, with dive bombers
then beginning to attack the Allied shipping in the area. As a result of the raid, the Dutch
troop transport Van Heemskerk would be beached after suffering several hits which set it ablaze;
the British cargo ship Gorgon would also be bombed and set on fire, although the blaze would be
extinguished later on; and the Dutch transport Van Outhoorn, as well as the Australian minesweepers
Wagga and Kapunda, would be damaged by near misses. The air duel, meanwhile, resulted in
eight Japanese aircraft destroyed; one Kittyhawk shot down; four more P-40s heavily damaged;
and one Lightning being forced to crashland. At Rabaul, the returning aircrews would then report
another series of hugely inflated results: three large transports and one medium transport sunk,
six transports heavily damaged and set on fire, and 44 Allied planes shot down for certain.
Though Yamamoto had planned to carry out an additional fighter sweep on April 16,
reconnaissance flights would fail to turn up adequate targets on New Guinea’s northeast coast.
This finally brought an end to Operation I-Go, as Japanese losses were mounting up and the
already-launched attacks appeared to have been a great success. Yamamoto and his staff were highly
encouraged by the deceptive reports submitted by the aircrews, completely believing that
the Allies had suffered tremendous damage. In reality, however, the air offensive had
failed to inflict serious damage on Allied forces . The only real consequence of Operation I-Go was
that American operations in the Solomons were set back about ten days, with bombing and minelaying
sorties being postponed to hold back aircraft in case the Japanese launched more air strikes.
Had the Japanese followed up on this offensive with more air raids, they might have succeeded
at their objective of preventing the future invasion of the central Solomons, but alas,
this would not be the case. Yet the most important consequence would be Yamamoto’s decision to carry
out a tour of the forward area in order to raise the morale of the men stationed there, just as he
had done in Rabaul; an action that would have a dire effect on the future of the Japanese Empire.
On April 17, Vice-Admiral Ugaki Matome, Yamamoto’s chief of staff, would also chair a conference to
review the lessons learned from the aerial offensive, notably including the tendency
of Japanese warplanes to catch fire after just a few hits with incendiary or even tracer rounds.
With the conclusion of Operation I-Go, a positive mood spread outwards in Rabaul once again
after so much time, resulting in an atmosphere reminiscent of the early days of the Pacific War;
but unfortunately for the Japanese, this boost in morale would be brief, as we’ll see in a couple
of weeks. Next episode, we’ll instead head back to the North Pacific and to CBI for the coverage
of some new and exciting developments in these two often-overlooked theaters. If you want to
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