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.
IF ARIIZUMI 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-400s. 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.
* According to some accounts, it took almost twice as long to prep the third Seiran.
† Robert Mikesh says seven minutes were required to launch each of the first two planes. See Mikesh, Aichi M6A1 Seiran, p. 13. Nambu, however, says all three planes could be launched in ten minutes.
‡ Sato, in Maboroshi no Sensui Kubo, says the third Seiran required 15 minutes to launch (p. 143). Nevertheless, it was a considerably longer period than for the first two aircraft.
§ The pilots called hazard pay pong roku because pong was the sound the catapult made during launch and roku means “six.” Interestingly, the hazard pay was capped at five launches no matter how many launches a Seiran pilot undertook.
CHAPTER 26
THE TASTE OF PERSIMMON
ARIIZUMI CONSIDERED THE SEA OF JAPAN 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.
WHEN 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:
“Cancel it, we don’t have time.”
Fujimori probably expected some resistance. The mission’s usefulness had been questioned before. But it’s doubtful he expected the attack to be canceled. Fujimori had devoted several years of his life to chaperoning the Panama Canal mission through the naval bureaucracy. Ariizumi had even called to tell him they were finally ready. Now, everything they’d worked for vanished in one meeting.9
There was one person, however, who refused to accept the verdict: Ariizumi. He continued to champion the attack despite Iura’s efforts to dissuade him. He made all the necessary arguments. His fleet was ready; the pilots had trained on a special mockup of the canal; they could leave immediately. But the plan to attack the canal was officially over. In its place, Ariizumi proposed attacking San Francisco or Los Angeles.10
At first the idea seemed foolish. What was the point of attacking an American city this late in the war? Ten Seiran bombers could hardly do enough damage to hurt the Americans. Ariizumi wasn’t crazy though. He was angry—angry and proud. Attacking Los Angeles might only inflict one ten-thousandth of the damage that American bombs had inflicted upon Japan, but it would demonstrate the Sixth Fleet’s resolve.11 Even a single arrow shot in the heart of an American city was worth the risk if it proved the fighting spirit of Japan’s submarine force.12
As Ariizumi viewed it, bombing the American people would be payback for the mayhem American B-29s were inflicting on Japan. It was also a way to show that his Sen-toku subs were a force to be reckoned with. After all, Ariizumi’s honor was at stake. And if everyone died on the mission, well, what a glorious finale it would be.13
Ariizumi gained some support among Sixth Fleet officers for attacking a west coast city. First, Chief Staff Officer Hanku Sasaki signed off. Then the Sixth Fleet’s sixth and final commander in chief, Tadashige Daigo, gave his assent. Since the Naval General Staff also had to approve, Ariizumi headed to Tokyo to plead his case.14
The historical record is muddled when it comes to the debate over target selection. According to Captain Nambu, Ariizumi was unwilling to abandon the Panama Canal mission and went to Tokyo to fight for its resurrection.15 Tsugio Sato, who seemed to know Ariizumi as well as anyone, says the issue of attacking San Francisco or Los Angeles had been settled before Ariizumi went to Tokyo. Whatever the sequence of events, attacking the Panama Canal versus American west coast cities was probably discussed after the Ministry and Navy General Staff votes, even if only for a short while.
Interestingly, there has been speculation that the Seiran were to be replaced by manned, jet-propelled suicide rockets.16 Such a weapon, the Model 43A, with folding wings for submarine launch, was in development at the end of the war. Though there is no evidence it was specifically intended for the I-400s, it’s possible it was considered, given the extreme thinking the Japanese High Command was capable of. There’s also been speculation that if Ariizumi had been permitted to launch a west coast air attack, his Seiran air group would have carried a “dirty” bomb.
The theory can be traced to a German U-boat, the U-234, which departed Kiel, Germany, in March 1945 destined for Singapore.17 The sub carried a special cargo in her mine storage area: ten lead-lined boxes containing uranium oxide.† Destined for the Japanese Army, the radioactive material was allegedly paid for by a shipment of gold sent to Germany aboard the I-52. The two tons of gold were in exchange for Nazi weaponry, including the Me 262, the world’s first jet-powered fighter, and the U-234’s uranium shipment.18 Some historians claim the radioactive material was destined for a dirty bomb to be dropped by Seiran aircraft over San Francisco or Los Angeles.19 The claim is based largely on conjecture, and supporting evidence is thin at best. It doesn’t help that the gold payment never reached Germany. The I-52 was sunk off the west coast of Africa, taking the gold shipment with her. In any event, Hitler died while the uranium was in transit, the two Japanese officers guarding the material committed suicide, and the U-234 surrendered to the U.S. Navy.20 In other words, the uranium never reached Japan. It’s conceivable (though unlikely) that the material could have arrived in time for Ariizumi to launch a west coast attack, if indeed this was even its purpose. But as events transpired, Ariizumi didn’t need to make dirty bombs. The Naval High Command had other plans for him.
THE SUMMER OF 1945 was exceptionally hot in Japan.21 The air was so humid, it felt like a wet woolen overcoat, and the relentless buzzing of cicadas made the atmosphere seem even more oppressive.
Ariizumi boarded the Shinetsu train accompanied by Lieutenant Funada for the long, convoluted trip to Tokyo.22 Even though militar
y personnel were given travel priority, the carriage was crowded.23 The train was traveling under blackout conditions, and Japan’s narrow-gauge tracks made for a bumpy ride. As if a hot, swaying train carriage weren’t enough, Allied bombs threatened the trip every step of the way.24 When Ariizumi finally reached his destination, he must have been tired indeed.
By June 1945 few buildings were left in Tokyo. Curtis LeMay’s bombing campaign had nearly wiped the city off the map. Hotel accommodations were especially scarce, so Ariizumi stopped in Shizuoka to spend the night with his family. Unfortunately, an incendiary raid the day before had reduced the town to ashes.
When he arrived at Shizuoka station, Ariizumi must have wondered whether his house was still standing. Smoke filled the air, and the burned-out ruins of the largely wooden city lay collapsed in the streets. Ariizumi’s house was near the army parade grounds; there was little reason to expect it had survived. When he arrived at his street corner though, the house was still standing.25 It was a miracle.
Ariizumi’s mother and his wife, Matsu, greeted him at the entranceway, along with his five children. It was a glorious homecoming. Ariizumi had not seen his family for some time, and he missed them terribly. Matsu expressed her deep appreciation for her husband’s safe arrival, even if it was only for one night. While she attended to his every need, Ariizumi’s children scampered about, excited by their father’s return.
That night Matsu prepared a sumptuous dinner.26 As Ariizumi ate his fill he probably contemplated the family garden a few feet away. A persimmon tree grew there. The Japanese describe the bittersweet flavor of its fruit as tasting like the memory of first love, a poetic if somewhat sentimental association. Persimmons were popular in Japan. They were looked forward to like summer corn in America or the first apples of the fall season. One wonders whether Ariizumi expected to live long enough to taste its fruit, especially since persimmons didn’t ripen until the fall. He’d certainly had his share of bittersweet experience. Given the way his war was going, it was unlikely he’d live to see his persimmon tree bloom.
Operation Storm: Japan's Top Secret Submarines and Its Plan to Change the Course of World War II Page 24