Operation Storm: Japan's Top Secret Submarines and Its Plan to Change the Course of World War II (35 page)

Taking off from a sub was always dramatic. The catapult was noisy,
¹⁸
but the actual launch was smoother than what Asamura was used to.
¹⁹
Its concussive force still slammed him into his seat back though. As the
Seiran
hurled down its track toward the tapering bow, the giant sub must have seemed not quite long enough to successfully launch an airplane. There was a sickening dip at the end, when the
Seiran
shot over the water and its engine clawed hungrily for altitude. An experienced pilot knew to gun the throttle for the lift he needed. For Asamura, it was the greatest ride he’d ever experienced.

The
Seiran
was one of the most cutting-edge planes of its day. Asamura was especially impressed by its gyro compass. Not even IJN surface ships had such a modern device. Though the initial
Seiran
were well made, quality dropped off as production fell. But as far as Asamura was concerned, the
Seiran
rivaled the best bombers the IJN had to offer. He just couldn’t get enough of that plane.
²⁰

As launch times improved, the 631st turned to bombing the Panama Canal mockup. The workshop at Maizuru Naval Base had built a full-size wooden version of the Gatun gates, based on blueprints Ariizumi had provided. When the mockup was complete, it was towed on a raft by tugboat to Nanao Bay, where it was anchored between two buoys.
²¹

The
Seiran
were dwarfed by the immensity of the structure. They were like flies dive-bombing a bowling alley. Skimming across the ocean surface at high speed takes skill, something many of the pilots still lacked. Nevertheless, they flew toward the mockup in a shallow attack hitting a top speed of 184 mph before breaking off at the last second and repeating the exercise.
²²

There would be no turning back from the lock gates, regardless of how quickly their flying skills improved. It would be virtually impossible to ditch a seaplane without floats and a bomb attached. No matter what happened, the
Seiran
pilots were heading for destruction.

The secrecy about the suicide mission sickened Takahashi. There was no reason the air group couldn’t carry out an attack and return safely to the subs. Bombing a stationary target was far easier than attacking a moving ship, which was why Takahashi had lost all confidence in his commanders. If Ariizumi wanted to throw his life away on a mission that could succeed without the sacrifice, he wasn’t going to stand in his way—he’d already lost 120 classmates.
²³
One more death wouldn’t matter, not even his.

Training conditions continued to prove difficult. Night training was particularly hazardous, with weather their biggest problem. June is Japan’s rainy season, and the weather was so poor, the
Seiran
pilots were often grounded by rain or fog.
²⁴
A pilot can’t improve if he doesn’t fly, and every day that Asamura and his men spent sitting in their barracks was another day lost.

The
I-14
was especially hard pressed to catch up. The last of the four
Sen-toku
subs to be commissioned, the
I-14
had the least amount of training. Captain Shimizu pushed his men hard to make up for lost time, but there was only so much he could do. Once his sub’s engine broke down, costing them part of a day; another time a float on one of the
Seiran
was damaged. These incidents hurt his crew as much as the pilots, since both needed training.
²⁵
Practice was the best way to avoid mistakes. Without it, you were asking for trouble.

Finally, training progressed enough that the bay became too confining and Ariizumi moved them into the Sea of Japan.
²⁶
The launch crews benefited from the open water, but with pilot inexperience, mechanical problems, and poor weather, it wasn’t surprising when another
Seiran
crashed.

It was the morning of June 13, and Lt. Masuo Egami and his observer, WO Hisayoshi Kimoto, were ferrying a newly completed
Seiran
from the Aichi factory to Nanao. Weather over the Noto Peninsula had deteriorated to the point where the ceiling was 500 feet and visibility less than six miles. Given the poor conditions, Egami and Kimoto crashed into a nearby mountain. The plane disintegrated, and both men were killed.
²⁷
The 631st’s casualties were continuing to mount.

The two men were promoted posthumously, and a memorial service was held at a local Anamizu school. Ten
Seiran
flew over the ceremony to honor their sacrifice.
²⁸
Takahashi thought it a shame the two had died. He’d known Egami from Penang and had admired his modesty. He understood they had felt urgency to deliver their plane, but he wished they’d turned back instead of fighting the weather. The old saying was true after all: the good died young.
²⁹

The day after the funeral Lt. Yasuo Kishi and his observer, Takeshi Tsuda, went missing.
³⁰
Darkness had settled on the last day of flight training, as their
Seiran
flew over Toyama Bay. When Kishi and Tsuda failed to return to base, a search was organized. The
Sen-toku
subs scoured the surrounding waters for four days without finding evidence.
³¹
Later, the two men’s bodies washed ashore on a nearby island.
³²
Theories were rife over the cause of the crash. One crewman speculated the plane was shot down by U.S. aircraft.
³³
Another thought changing wind conditions might have been responsible.
³⁴
Whatever the reason, the loss was problematic. Nine men had died in five crashes, destroying three
Seiran
and two
Zuiun
. Additionally, another man had been killed when the
I-400
’s high-pressure tank had blown.
³⁵
The mission could not afford many more losses.

I
F
A
RIIZUMI HAD
any luck during this period, it was maintaining the secrecy of his goal. The
Sen-toku
subs were one of the most confidential weapons programs in the Imperial Japanese Navy. They had been carefully camouflaged during construction, and their existence was so secret that when a new crewman reported for duty, he was told no such sub existed.

Historians have claimed that U.S. naval intelligence knew nothing about the underwater aircraft carriers and little about their
Seiran
. Though it’s true that the United States knew nothing about the Panama Canal strike, they did know something about the
I-400
s. For example, in a U.S. naval intelligence document titled “Japanese Ship List: Know Your Enemy!” a description of the
I-400
and
I-401
appears on page 11. Since the document is dated December 18, 1944, it means the U.S. Navy knew about the
Sen-toku
squadron at about the same time they were commissioned. But there was knowledge of the subs even before then.

When the United States invaded Saipan in July 1944, it captured authorizations issued by Japan’s Navy Ministry detailing ship and submarine construction. In May 1945, while the
Sen-toku
subs were still bottled up in Kure, U.S. Naval Intelligence released a translated version of these documents, which listed where and when the
I-400
subs were being built.
³⁶

A June 1945 naval intelligence report also described the subs as carrying an airplane and potentially playing an offensive role. “These units may be used for long range supply and combat operations,” the reports states. “[And] it is believed that a scout observation plan is carried for reconnaissance patrol.”
³⁷
The subs might have been operational by the time the United States learned of them, but their existence was certainly known, if not their intended purpose.

The same held true for the
Seiran
. Though the United States never assigned Aichi’s M6A1 a code name, Naval Intelligence was aware that the plane existed. A 1944 report from the Allied Air Technical Intelligence Center indicates that the plane was of unusual design, flew 220 mph, and was intended for use with a submarine. The report even translates the plane’s name as “clear day.”
³⁸
Though U.S. Intelligence failed to identify the
Seiran
’s purpose as a special attack plane or its intended target, it’s clear the United States knew of its existence, even if the details of Ariizumi’s mission were unknown.

This means the
Sen-toku
subs were at risk, especially since U.S. code-breaking efforts rendered the entire Sixth Fleet vulnerable to attack. Once Ariizumi began reporting his sub’s coordinates, it would be easy to find and destroy him.

Unfortunately for Ariizumi, he counted on his underwater aircraft carriers remaining a secret.

A
RIIZUMI CONSIDERED THE
S
EA OF
J
APAN TO BE SAFE BECAUSE IT
had been for three years. But U.S. submarines had recently begun penetrating the Tsushima Strait’s mine-laden barrier. On June 9, while Nambu trained in the waters of Toyama Bay, the USS
Skate
(SS 305) entered the Sea of Japan along with eight other subs. The next day the
Skate
torpedoed and sank the
I-222
a short distance from where the
I-401
was practicing.

Inouye, the
I-401
’s sonar operator, happened to be on deck that day when a huge column of water rose into the sky.
¹
Nambu assumed that an enemy sub trying to enter the bay had hit a Japanese mine and sunk. He soon learned the truth though when the
I-222
failed to arrive at Nanao.
²

The
I-222
was an antiquated sub. Commissioned in 1927, she’d eventually been withdrawn from combat and used for training ever since.
³
Filled as she had been with green recruits, the consequences were both sad and predictable when she crossed paths with the USS
Skate
. There was little an unarmed sub could do against an experienced predator. The incident also demonstrated that the United States could kill Japanese “chicks in their nest.” Had the
I-401
been operating a bit farther north, it could have been her rather than the
I-222
that was sunk.
⁴
As it was, the
Skate
and her colleagues destroyed 28 ships during the next two weeks.

Clearly, the endgame had finally begun. The Sea of Japan was no longer safe.
⁵
Fortunately, the
Sen-toku
squadron’s departure for Panama was only a few days away. Importantly,
Seiran
launch times had improved significantly. Some accounts suggest all three planes
could be launched in as little as ten minutes, though this was probably without floats (if at all).
^*
6
Twenty to 30 minutes is a more realistic assessment, and even then it was only when everything went right. It was significant progress though. The special attack fleet had not only reduced their launch time,
Seiran
pilots were proficient enough to attack the Gatun lock. They were ready to embark on their mission.

If the
Sen-toku
squadron had reduced its window of vulnerability, its mission still relied upon surprise. As at Pearl Harbor, it had to reach the enemy undetected, or the mission would fail. Considering that four subs would have to travel the width of the Pacific, surface near where U.S. defenses might reasonably expect them, launch their planes in the middle of the night, and attack at dawn without being discovered, stealth would play a crucial role in their success.

Unfortunately, stealth was the only card they had left, because Ariizumi was about to receive some shocking news from the Naval General Staff.
⁷
The fall of Iwo Jima and the impending loss of Okinawa meant the enemy was on their doorstep. The war had passed the point where bombing the Gatun lock would make a difference. As a result, the mission to attack the Panama Canal was being scrapped. Instead, the
Sen-toku
subs were being assigned a completely new target.

W
HEN THE ATTACK
on the Panama Canal was canceled, Ariizumi was furious.
⁸
The
Sen-toku
subs had been training for six months, they’d overcome every conceivable obstacle placed in their way, and they were finally ready to bomb the canal. Furthermore, the purpose of the attack was to prevent the invasion of Japan. How then could it be canceled? The nation’s future was at stake. The news was too bitter to accept without a fight.

NGS Officer Shojiro Iura journeyed from Kure to Maizuru to fill Ariizumi in on the details. Sometime in early June, while the
Sen-toku
squadron was training, a meeting had been held with the Navy Ministry. NGS Senior Officer Yasuo Fujimori had made a presentation to Navy Minister Mitsumasa Yonai and other attendees, reviewing the attack plan. Shortly after Fujimori finished, he was told: