Operation Storm: Japan's Top Secret Submarines and Its Plan to Change the Course of World War II (8 page)

I
F AT THE BEGINNING OF
W
ORLD
W
AR
II
THE
A
MERICAN SUBMARINE
force was “as nearly equal to Japanese submarine strength as it was possible for coincidence to contrive,”
¹
by May 1942 the Sixth Fleet seemed invincible. Not only had Yamamoto’s sub force tightened the noose around U.S. shipping on the west coast, it had successfully bombarded continental America between Santa Barbara and Seattle. Add to this the attack on Pearl Harbor and Japan’s successful invasion of the Philippines, Malaya, Georgetown,
^*
Thailand, Singapore, Hong Kong, Rangoon, Guam, Wake Island, and the Dutch East Indies, and victory fever was at an all-time high. Though June would prove a bloody month for both sides, there seemed no stopping the Japanese in May 1942.

During this period, Japan’s naval air corps was the finest in the world. Mitsubishi’s A6M Zero fighter (Allied code name: “Zeke”) was partly responsible, as were Japanese pilots, who were well trained, battle hardened, and fearless. Some Japanese pilots were so macho they even dispensed with their parachute. The naval air corps, always a favorite of Yamamoto’s, was on a roll, and it was within this context that the architect of the attack on Pearl Harbor came to expect the impossible.

When the question was raised of whether an attack plane that would fit inside a submarine could be built, it was self-evident that the sub design had to be agreed upon before any plane could be specced. Otherwise how would anyone know how large, or small, to
make the aircraft, since it had to fit inside the sub’s hangar? Once again Yamamoto was asking for a lot.

The
I-400
’s mission required a plane that had speed and range as well as the ability to carry the largest bomb possible. These features were contradictory. You can make a plane fast, or you can give it range—when you try to do both and make it carry the biggest bomb on your shelf, trade-offs begin.

Adding to the complexity was the need to design wings that could fold small enough for the aircraft to fit inside a sub hangar yet be unfolded fast enough for a quick launch. This meant fewer detachable parts. Attaching things takes time, and the more time a submarine spends on the surface, the more vulnerable it is to attack. Eliminating loose parts and automating assembly became especially important considering the limited deck space the launch crew had to work with. It was a complicated problem, one that required ingenuity to solve.

Some early IJN floatplanes could be launched from a sub in as little as seven minutes. But once fuel and hydraulic lines were threaded through a modern monoplane wing structure, detaching them became difficult. On top of this, the aircraft was so specialized, it couldn’t be mass produced. This meant it needed custom building, which was slow and expensive.
^†
2

The IJN had a history of outsourcing design and production of its aircraft to private sector manufacturers.
³
So while the Air Technical Bureau discussed the aircraft’s specifications,
⁴
Naval Aviation Headquarters began secret talks with the Aichi Aircraft Company to design, test, and build the new plane.
⁵

Aichi received a formal request to develop the world’s first purpose-built attack plane to operate from a submarine on May 15, 1942.
⁶
Initially, the plane was named “17
-shi
Special Attack
Bomber”
⁷
because 1942 was the seventeenth year of Hirohito’s reign, and
shi
means “experimental.” Aichi would apply its own utilitarian designation before the plane went into production.
⁸
But an even more glamorous moniker,
Storm from a Clear Sky
, would follow after the first prototype was built.

Aichi was an interesting selection to manufacture the plane. Founded in 1898 as the Aichi Clock and Electric Manufacturing Company, Ltd., the firm didn’t get into the airplane business until 1920. By the early 1930s, Aichi had become the IJN’s fourth major aircraft supplier. The IJN split its business among larger companies like Mitsubishi, Kawasaki, and Nakajima for efficiency’s sake. But over time, Aichi became a “captured supplier,” building aircraft exclusively for the IJN.
⁹
The company’s most successful plane was the D3A dive-bomber (Allied code name: “Val”), which sank more Allied warships than any other Axis aircraft.
¹⁰
The plane’s devastating record at Pearl Harbor probably contributed to the selection of Aichi to build the
I-400
’s attack bomber. Either way, Aichi had the necessary experience.

The company’s design chief, Toshio Ozaki, was named project leader responsible for all aspects of the plane’s design and construction. Ozaki was closely identified with the 17-shi program,
¹¹
as were his two engineering assistants, whose job was to coordinate with the
I-400
’s design team to ensure that the sub’s support equipment and environmental facilities met the aircraft’s needs.
¹²
The humidity inside a sub is so great, it plays havoc with electrical systems. This was an important consideration, so Aichi paid close attention. Finally, Lt. Cdr. Tadashi Funada, the leader of Yokosuka’s seaplane group and a member of the Naval Air Arsenal’s Experimental Aircraft Department, worked closely with Aichi not only to design the aircraft but to serve as its chief test pilot as well.
¹³

The 17-
shi
was conceived as a one-mission attack bomber,
¹⁴
no return, no deposit. Floats would be dispensed with (except for practice flights), not because a suicide mission was planned (those wouldn’t become standard for another three years) but to maximize
the plane’s range and speed.
^‡
15
After completing the mission, the aircraft’s crew would rendezvous with the
I-400
, ditch the plane, and swim to the sub to be picked up. Presumably nobody thought a second act could top bombing New York and Washington.

The design called for two flight crew seated tandem style: a pilot in front, who acted as bombardier, and an observer in back, who acted as radioman, navigator, and tail-gunner, and made the calculations necessary to set torpedo depth. Since the aircraft not only had to get to its destination but had to defend itself along the way, the initial spec called for two machine guns: a fixed, front-facing 7.7mm gun and a rear-facing 13mm Type 2 gun.
¹⁶
The rear-facing machine gun was belt fed and handled 300 rounds.
¹⁷
Flexibly mounted, it folded down when not in operation and locked against the plane’s starboard fuselage. When the gun was required, the observer swiveled his bucket seat 180 degrees to face backward and slid open the cockpit’s overhead canopy, automatically raising the gun into firing position—a pretty neat trick.

It soon became apparent that the 17
-shi
would have trouble outrunning an enemy fighter. The plane’s defensive armament wasn’t satisfactory either. In the event of an attack, it would require luck or damn fine piloting skills to survive. But nobody was complaining. Early versions of the Zero fighter had neither armor plating nor self-sealing fuel tanks in the event of a puncture—both standard features on Allied aircraft. Since Japanese pilots were famous for their courage, neither speed nor lack of armor seemed a problem.

Like many planes of its day, the special attack bomber had an aluminum alloy airframe, with wood limited to the instrument panel and wingtips.
¹⁸
The control surfaces, namely the tail’s vertical and horizontal stabilizers, were fabric covered, yet the overall plane was solidly constructed.
¹⁹
As one pilot who later flew the aircraft
said, “It was the most cutting edge plane of its time,”
²⁰
and indeed, the special attack plane was destined to become not only Japan’s most advanced and complex aircraft of the war
²¹
but its highest-performance floatplane in terms of payload and speed.

To keep things simple, Aichi looked at converting one of its own aircraft to do the job. The plane that made the most sense was the D4Y1
Suisei
, a carrier-based dive-bomber (Allied code name: “Judy”). Aichi had recently begun mass production of the
Suisei
, and the company hoped it could be adapted for use aboard the
I-400
with few modifications; Aichi probably realized that the best way to save money was to share the major assemblies of two aircraft.
²²
Unfortunately, the
Suisei
proved less adaptable as a sub-based plane. It may have been considered the IJN’s best single-engine bomber of the Pacific war,
²³
but it couldn’t be made to fit in the
I-400
’s hangar.
^§

Research, design, and testing of the
I-400
’s aircraft would consume Aichi for the rest of 1942 and most of 1943,
²⁴
and like everything else about the project, the schedule was ambitious. The
I-400
subs were designed to carry two attack planes each. Given 18 subs, this meant constructing a minimum of 36 planes.
²⁵
But 36 planes were not enough, because trainers and replacement aircraft were also needed. The goal, then, was to construct a total of 78 planes, 44 in 1944 and another 34 in 1945.
²⁶
The size of the order confirms just how important the IJN viewed the
Sen-toku
squadron.

But the first step was to develop a design that addressed the complex balance among size, weight, range, speed, and payload yet still allowed the plane to be folded into a small enough package to fit inside a sub hangar. That the hangar was only 11 feet 6 inches in diameter
²⁷
made the job more challenging, since many propeller blades were longer than that. It wasn’t going to be easy.

A
S MIGHT BE
expected, the history of plane-carrying subs is an unusual one. At least six countries experimented with sub-plane combinations with varying degrees of success, but only Japan was able to carry the idea to fruition. Perhaps Japan’s success was due to understanding the benefits of a sub-plane combo better than other nations, or perhaps she had the greatest need. Whatever the reason, Japan was to spend nearly 20 years perfecting the combination, when other countries had long since given up.

Both the British and Germans tested a floatplane-submarine combination during World War I. The Germans did it first in January 1915, when a floatplane pilot teamed up with a U-boat captain he’d met socially to conduct aerial reconnaissance of an English town.
²⁸
The German High Command was not impressed, and no additional flights were made.

The HMS
E-22
was another early example. A British E-class submarine commissioned in 1915, she carried two Sopwith Schneider seaplanes on deck to intercept and destroy German Zeppelins.
²⁹
The Admiralty had originally considered the idea of plane-carrying subs inhumane, but Zeppelin raids on London soon changed that notion. The first trial of the
E-22
was conducted in the North Sea on April 24, 1916. Submerging the boat in a calm sea, the Sopwith Schneiders floated free and took off for England, proving the concept worked. The trial was not repeated because two days later the
E-22
was torpedoed by a German U-boat. There were no survivors.

During the early days of sub-plane experiments, subs and floatplanes were used with a minimum of modification. The aircraft was carried on the sub’s deck, but there was no means of housing it and no way of retrieving the plane once she departed.

The United States began experimenting with its own version of a plane-carrying sub in 1923. The
S-1
had a small on-deck storage container that housed a Martin MS-1.
³⁰
Unfortunately, before the plane could be launched, 16 man-hours were required to put it together.
³¹
This made the Martin MS-1 about as popular as an unassembled toy on Christmas Eve. Once the aircraft was ready, the sub
submerged enough to allow the plane to slip off its stern and take off in the water. The eventual launch must have been anticlimactic given the prep time.

The goal of the
S-1
was to use its plane to scout ahead of the fleet and report back on the enemy’s position.
³²
But as submarine expert Norman Polmar explains, “The U.S. had enough dirigibles and carrier planes that they didn’t need to experiment with plane-based submarines.”
³³
It was no surprise then when the United States abandoned the program in 1927.

Britain picked up the gauntlet that same year with the M-2, also known as a “mutton boat” because its 12-inch gun and turret resembled a leg of lamb. The M-1’s first captain, Max Horton, was an early proponent of sub-borne airplanes. As a result, the
M-2
had its gun removed and was refitted with a floatplane hangar, a compressed air catapult, and a crane for loading and unloading aircraft.
³⁴