...The conventional narrative on the Pacific War has it that Japan never intended
to invade Hawaii. This view asserts that the Japanese leadership felt Hawaii was
too difficult to capture and retain and that it was in any case outside the desired
limits of the Greater East Asia Co-Prosperity Sphere.49 However, we now know
that Hawaii was in fact explicitly included within the sphere in both public and
classified wartime documents and was the focus of Genda’s thinking from the
beginning.50
Genda understood that Pearl Harbor was the headquarters of the Pacific
Fleet, a crucial logistics and repair facility, a vital intelligence center, and an ideal
springboard for any counteroffensive against Japan. Hawaii was also the anchor
for air and maritime communications between the United States and the southwestern
Pacific. From the moment Genda began preparing his draft, he favored
a full-scale landing of Japanese troops on Oahu. “We should follow up this attack
on Hawaii with a landing,” he said. “If Hawaii is occupied, America will lose her
largest and best advance base and, furthermore, our command of future operations
will be very good.” American fighting forces on Hawaii would have to retire
to the West Coast, and Japan would dominate the Central Pacific.51 Genda’s conceptualized
plan, that is, took Yamamoto’s intent one step farther—to take Pearl
Harbor away from the Americans and thereby eliminate their ability to project
power from the Central Pacific. Once in Japanese hands, the Hawaiian Islands
could be used militarily to threaten the continental United States and, politically,
as a bargaining chip in negotiations to end the war.52 The key to Genda’s vision
was not what Japan would gain by acquiring the islands but what the United
States would lose.
It is in this plan that the true nature of Genda’s operational-level thinking is
manifest. Genda believed that without seizing and holding Oahu, Japan could
not hope to win the war. Oahu had to be taken at the outset of the conflict, while
surprise and initiative still worked in Japan’s favor. Once it had been occupied,
conditions would be favorable for subsequent operations in the south, and Japan
would have time to figure out how to maintain and resupply the islands. Genda
believed that Hawaii, not the Philippines, should have been Japan’s major military
objective at the outset. Where Yamamoto saw a delaying action, Genda saw
a knockout punch—the annihilation of the enemy’s operational center of gravity
with one decisive, joint operation.53
Assuming that the initial air strikes were successful and that the Japanese had
air superiority and given intelligence estimates of approximately two American
divisions on Oahu, Genda believed ten to fifteen thousand well equipped troops
would suffice for its capture.54 Genda realized the risks involved in moving a large
task force across the North Pacific to attack Oahu, but he felt that even if (as the
Japanese expected) a portion of the force was destroyed, the loss of shipping and
troops would not materially impact operations in the south.55
Predictably, so innovative a plan, coming originally from a mere commander
(though possibly over the signature of a rear admiral), did not survive contact
with the senior planners of the Combined Fleet staff, particularly at a time when
the concept of a carrier air attack, backed by Yamamoto himself, was itself experiencing
stiff opposition. But during naval war games to test the planned Phase
One operations in September 1941, the idea of invading Oahu resurfaced. In
preparation for the event, Commander Watanabe conducted a detailed study of a
possible invasion of Oahu. He estimated that a successful invasion would require
at least two Japanese divisions, about thirty thousand men. Transporting them,
with their equipment and supplies, would require eighty transports and escort
vessels, including thirty-two destroyers, eight cruisers, four battleships, two aircraft
carriers, six to eight submarines for reconnaissance, and ten tankers. These
would be in addition to the carrier strike force.56
Watanabe laid out two landing sites: one on the northwest coast on both sides
of Haleiwa, the other in the area of Kaneohe Bay. The southern coast was best
suited to an invasion, but it was also the most heavily defended area of Oahu. The
west coast was eliminated, because the U.S. Navy had held invasion maneuvers
off the west coast a year before, and the Americans were likely well prepared to
defend that part of the island.57
The two landings would happen simultaneously at midnight of 7/8 December.
Half a division would land at Haleiwa, to take Schofield Barracks. The objectives
of this attack were not only to take the barracks but to draw American forces
northward, by giving the impression that it was the main effort. The actual main
attack, however, was planned for the east coast, at Kaneohe Bay, with one and a
half divisions. Two-thirds of this force would occupy that, the remainder the region
below Laie. The objective was to cross the Koolau Range, using horses, and
then descend on Pearl Harbor, cutting off any retreat to the mountains of Oahu.
The Japanese knew from intelligence that the Koolau mountains were not fortified
and in fact were open to the public. Given complete air superiority, Watanabe
estimated, it would take from two to four weeks to capture the island.58
Watanabe tried to discuss the study with Captain Kuroshima but the latter
was not interested, considering an invasion infeasible and to be going against the
concept of operations for Phase One. After the war, Kuroshima would declare
that the “biggest mistake” of his life was this refusal to consider invasion of Oahu
after the carrier attack.59 Genda’s and Watanabe’s superiors, for their part, always
considered the idea in the context of the invasions of the Philippines and Malaya,
also to be accomplished at the outset. Considered accordingly, an invasion of
Oahu was easily dismissible from a resource perspective. Genda himself, in contrast,
viewed the invasion as either instead of or before the Philippine operation,
with the intent of denying American ground, sea, and air forces the use of the
Hawaiian Islands as an advance base.
Regardless, any invasion of Oahu would have needed the support of the army,
which was firmly focused on China and willing to provide only the smallest
number of divisions necessary to acquire the territories identified in Phase One.
In fact, the IJA planned to commit only ten of its fifty-one divisions and four of
its fifty-nine brigades to the Southern Army for these operations.60 Notably, however,
and reflecting the important role envisioned for airpower, the IJA allotted
seventy of its 151 air squadrons to support the Southern Operation.
The mistrust that existed between the two services is evident from the fact that
the Combined Fleet never approached the IJA to discuss a Hawaiian invasion option.
The Combined Fleet was so concerned with the secrecy of the Pearl Harbor
carrier attack that it did not want to divulge the plan to the army. The Combined
Fleet’s fear was based on the IJA’s strong influence over governmental decision
making—if the IJA objected to the attack, it could easily force its cancelation.
Watanabe lamented that “once they [IJA] rejected something, nothing could be
carried out.”61
For all these reasons, and despite repeated attempts by Genda to drive home
the importance of taking the islands, the idea of invading Oahu as part of the
initial attack was dead. Knowing that there was no stomach for invading Oahu as
he had wanted, Genda moved to the next best course of action available, which
was to design a plan that would deny Pearl Harbor to the Americans, through the
destruction of the base and its facilities. “In my opinion, Japan had to neutralize
American bases in the Pacific if she was to carry on the war successfully.”62
Genda’s modified plan involved repeated attacks against the infrastructure of
Pearl Harbor and the Pacific Fleet at its moorings, and a possible fleet engagement
against any American warships found outside the harbor. A significant problem
for Genda was that Vice Admiral Nagumo, who commanded the 1st Air Fleet,
had little faith in or understanding of naval airpower or the potential of the air
arm at his disposal.63...
