NO. 8: AFT COMPARTMENT The last compartment inside the I-401 was her largest. Located in the stern, it was the crew’s aft berthing compartment. Here the sub’s interior hull gave way to a 61-foot-long space, the widest in the sub and second in size only to her aircraft hangar. U.S. subs usually reserved their aft compartment for a stern torpedo room, but the I-401’s held sleeping quarters, a head, various steering mechanisms, and an emergency signal ejector to let rescue ships know where the sub had gone down.99
The aft compartment was slightly more relaxed than the rest of the sub, in part because it was the area least likely to be visited by an officer. Crew members entering the compartment removed their shoes before stepping onto a raised wooden deck. So many feet rubbed the wood planking that it soon became as polished as a dance floor.100
BATTERY COMPARTMENT Below the I-401’s habitable space was a second world, where the sub’s inner workings were housed. It was a dark, dank place that included the pump room, the ventilation exhaust blowers, the lubricating and freshwater tanks, the anchor chain, ammunition storage, and a considerable number of valves and piping: it was no place for a man suffering from claustrophobia.
The I-401’s life-giving battery cells were located here. Made of lead and containing sulfuric acid, each cell weighed more than 100 pounds. These cells were used when the sub was submerged to power the electric propulsion system. Batteries could prove a liability, however, especially if contaminated by saltwater, which produced fumes that could overwhelm a crew. There was also a chance, when the batteries were recharging, that hydrogen might build up and ignite. Not surprisingly, batteries were checked as often as a boat’s powder magazine, since an explosion in either could scuttle the sub.
U.S. subs were hardly five-star hotels, but they were downright luxurious compared to the I-401 and a lot more reliable. For example, the Segundo had three showers, four heads, and more than half a dozen sinks for 70 men, while a typical I-boat would have considerably fewer bathroom facilities for more than twice the crew. A Balao-class sub not only had what a Japanese I-boat captain would have considered an impressive number of bathroom facilities, it also had a top-notch air-conditioning plant. And if that didn’t ensure a crew’s comfort, there were an ice cream freezer, a film projector, a sunlamp in the engine room, steak on the menu, and a washing machine that used too much water. There was even an escape hatch in case the sub went down, although most submariners had little faith it would work and insisted its only purpose was to placate their mothers. These were inconceivable luxuries for a Japanese sub captain like Nambu. Sixth Fleet submarines were at war—sunlamps had nothing to do with it.
IT WOULDN’T HAVE taken long for Nambu to conclude that his sub’s huge size reduced her maneuverability. Anything that increased a sub’s dive time or diminished her operational capacity was frowned upon. So though the I-401 was fast both above and below the surface, her dive time (not to mention her ability to stop promptly) was compromised.
Another problem was the sub’s sail. The fact that it was offset to port created an unbalanced form of drag when the sub was submerged. It was as if the front wheels of a car were permanently out of alignment. A helmsman had to steer a seven-degree starboard course at two knots submerged just to follow a straight line. Additionally, the offset tower meant the sub required a larger starboard turning radius when underwater.101 Nambu would shrug off these difficulties, but they’d be constant worries for his helmsmen.
After Nambu’s inspection of his new sub, he likely drew the following conclusions: the I-401’s high freeboard, broad beam, and deep draft would make her a comfortable boat in a seaway; her hull shape would naturally reduce roll and pitch, and her bridge would remain dry under most weather conditions; and though her safety depth was only 328 feet (82 percent of her overall length), she was fast and well armed.102 Yes, size reduced dive time and maneuverability, which made her lumbering, but she could certainly defend herself.
When Nambu finally exited the I-401, his heart pounded with a sense of expectation. He would soon command a sub that the Imperial Japanese Navy had staked everything on.103 That he would lead her on a top secret mission designed to change the course of the war only added to his pride. Though he knew his chances for success were slim, Japan’s future rested on his shoulders. He would complete the mission or die trying. There was no turning back.
* The actual distance was six feet ten inches.
† Nambu recalled that the crane was able to lift 3.5 tons, but he was probably wrong about this. A Seiran weighed approximately 7,300 pounds without pilot, observer, or fuel. Fully loaded, she weighed close to 10,000 pounds. As a result, the lifting capacity of the I-401’s crane was probably at least 5 tons and may have been as much as 12 tons. See Nobukiyo Nambu, Beikidoukantai wo Kishuseyo: Sensuikuubo I-401 Kanchou No Shuki [Surprise Attack on the American Fleet! Memoir of the I-401 Aircraft-Carrying Submarine by Its Captain] (Tokyo: Fuami Shobo, 1988), p. 180.
‡ According to Nambu, the I-401 had 204 officers and crew. Nobukiyo Nambu, Beikidoukantai wo Kishuseyo: Sensuikuubo I-401 Kanchou No Shuki [Surprise Attack on the American Fleet! Memoir of the I-401 Aircraft-Carrying Submarine by Its Captain] (Tokyo: Fuami Shobo, 1988), p. 221. The I-400 carried fewer crew.
§ The access tube was 20 inches in diameter and had both upper and lower hatches.
CHAPTER 18
THE 631ST
AS 1944 DREW TO A CLOSE, THE I-401 REMAINED UNFINISHED. Nearly two years had passed since the sub’s keel had been laid. Katayama’s timeline had proved optimistic. Although the Sasebo naval yard was working around the clock, the flagship was still behind schedule.1
It was important to maintain crew morale in the face of such a delay. To this end, Nambu commissioned a ship’s song. Usually, individual vessels didn’t have an anthem. The I-401 was an unusual case.2 Nambu asked his crew for lyrics. Then, after editing their contributions, he had the Sasebo Naval Band set them to music. When it came time to rehearse, his crew lustily sang their flagship’s new song.
Symbolic rituals required a surprising amount of Nambu’s attention. They were necessary though to preserve IJN tradition. For example, every IJN ship had an onboard shrine where the crew prayed for success. The I-401’s primary shrine was in the control room. But a statue of Ise, the spirit who watched over submariners, was needed to fill the niche. Fortunately, the Grand Shrine at Ise, one of Japan’s most sacred Shinto sites, was nearby. Nambu also needed a written fortune for the sub, to reassure the crew about their future. Too busy to get it, he sent his chief navigator to fetch one instead.3 Sometimes superstition was more comforting, especially when logic suggested something less satisfying.
The Imperial Japanese Navy officially organized the Sen-toku subs into SubRon 1 on December 15, 1944.4 The next day the I-13 was completed.5 Captained by Cdr. Katsuo Ohashi, the I-13 immediately departed for her shakedown cruise in the waters off Kobe.6
Ohashi was the third Sen-toku captain to have served in the Indian Ocean. It’s not clear whether he knew Ariizumi personally. Still, he’d sunk a fair number of Allied merchant ships as skipper of the I-56 (later the I-156). Interestingly, when he came across Australian airmen in a lifeboat in 1942, he declined to massacre them despite his officers’ entreaties.
“The war situation won’t be affected,” Ohashi told them. “Let’s not partake in any senseless killing.”7
Fourteen days after the I-13 was commissioned, the I-400 was also handed over. It was just two days before the New Year,8 and the I-401 still wasn’t ready. Nambu could only wait enviously as his sister subs headed out to sea.9
AT THE SAME time SubRon 1 was being organized, the 631st Kokutai, or air group, was formed with Ariizumi in command. Ten Seiran bombers, three for each of the two I-400 subs and two for the I-13 and I-14, respectively, would form the heart of the unit, with additional Seiran for training and replacement. It was a much-reduced force compared with Admiral Yamamoto’s original vision. Yamamoto’s plan had called for 18 subs and 44 Seir
an before the underwater aircraft carriers had been reduced in number. By June 1944 Aichi had completed a measly four Seiran, with a production capacity limited to one per month.10 This meant that only ten Seiran would be ready by the end of the year, far short of the modified goal.11 And two of these weren’t even combat aircraft, they were trainers. As a result, when the Sen-toku subs began launching in December, not one Seiran was ready for assignment. They were still undergoing flight testing.12
Engine problems were partly responsible for the slow pace of Seiran production.13 You couldn’t do anything without a reliable engine, which led to a cascading series of consequences. Shortage of aircraft meant flight tests were delayed, which in turn meant fewer planes were available for pilots to qualify in. Additionally, more and more pilots were being transferred to Yokosuka in anticipation of the 631st being formed. When new pilots arrived, they had to make do with alternative floatplanes like Aichi’s Zuiun, which they disparagingly referred to as a “toy.”14 Frustrations mounted.
The situation was further complicated by the surface fleet, which got first dibs on experienced pilots.15 There were so few aviators with combat experience this late in the war that many of the 631st’s pilots were green. Almost none of the new arrivals had the dive-bomb experience necessary to attack the Panama Canal.16 Though specialized training could make up for the shortfall, they had to have planes to train in, and that continued to be an issue throughout the winter months.
Ens. Kazuo Takahashi was one of the first pilots to show up for Seiran instruction. Confident and handsome, Takahashi had been a seaplane instructor when the war started and later became a floatplane pilot aboard the 1–37.17 It probably wasn’t a coincidence that he’d been assigned to the 631st, since he’d known Ariizumi when they’d served together in SubRon 8.
Takahashi had never even seen the ocean before enrolling in the navy’s Junior Pilot Training Course,18 yet by the time he arrived at Yokosuka Naval Air Station, he was a veteran pilot. His seaplane experience made him an ideal choice for a Seiran pilot. When Takahashi arrived at Yokosuka on August 24, 1944, he was given a Seiran instruction manual and told to read it. A week later he donned his flying helmet lined with rabbit fur and flew his first Storm from a Clear Sky.19
Takahashi began flying Seiran in September. He measured takeoff, landing, ascent, and cruising speeds, as well as fuel consumption and descent rates. There was also some formation flying. What Takahashi liked best though was testing the Seiran’s responsiveness. The plane handled so well, he soon fell in love.20
By mid-September, Takahashi was flying the Nanzan, or land version of the Seiran. He found the plane lighter and faster than the sea-based version.21 He especially enjoyed its acrobatic abilities, finding it handled as well as a Zero fighter,22 high praise considering the plane was merely an attack bomber.
Come October, Takahashi was ready to begin torpedo training. After learning how to operate the bombsight, he took to the air over the Otake target range carrying a torpedo. Dropping to an altitude of only 100 feet, he skimmed across the ocean at breakneck speed. Centering the target in his bombsight, he pressed the drop activation switch just below the grip on his control stick. When the torpedo fell, a miniature light verified its release.23 Takahashi already knew that it had dropped though—because his plane leaped 60 feet into the sky.24
Takahashi watched with anticipation as his torpedo raced toward the target. After 300 feet it inexplicably slowed, veered to the left, and began emitting smoke. He was crestfallen—he’d expected it to explode. He didn’t realize it was a dummy.25 Takahashi had one more chance to practice dive-bombing that month, but he would need a lot more training before he became an expert.
By November 15 engine production had improved enough that Takahashi was sent to collect another Seiran from Aichi’s factory.26 Aichi’s skunkworks were in a stand-alone building separate from its main plant.27 Seiran were built in a large steel-framed hangar with a curved roof, floor-to-ceiling windows, and metal support columns that looked like bridge trusses. Built one at a time, it was a customized approach compared to the assembly lines favored by the United States. It was the best Aichi could do given the specialized nature of the aircraft.
When Takahashi arrived, Aichi’s assembly facility had a poster on the wall reading, “Let’s pull together!”28 High school students were building much of the plane by hand. The Ministry of Education had suspended classes so students could work in war production.29 Many of the workers were girls 12 to 15 years old,30 which resulted in some unexpected consequences. One Seiran fuselage was found to have a drawing of a Japanese woman scratched in its surface—not exactly regulation markings for a combat aircraft. The system worked though and to prove it, two new Seiran stood ready for Takahashi to fly.
LT. ATSUSHI ASAMURA arrived at the Yokosuka seaplane base in November 1944. Twenty-two years old and small for a pilot,31 he had no trouble fitting into a cockpit. He was already a seasoned flyer—his specialty was twin-seater seaplanes. Like Ariizumi, he was an Etajima graduate,32 but he was more senior and had taught at Kashima Naval Air Station. Most recently he’d been an aircraft officer aboard the cruiser Aoba.33 When the Aoba was severely damaged during the Battle of Leyte, Asamura was transferred to Yokosuka. There were never enough experienced seaplane pilots to go around.
Asamura was on the tarmac when he noticed a bright orange aircraft buzzing in the sky overhead.34 The color designated an experimental plane, which naturally piqued his curiosity.
“What’s that?” Asamura asked Lt. Cdr. Tadashi Funada, the Seiran’s first test pilot.
“It’s the most secret of secret planes. It’s called Seiran, and we only have two so far. Once we’ve manufactured thirteen, we’ll load them onto submarines and bomb the Panama Canal. You’re going to be the flight leader.”35
Asamura’s chest swelled with pride. Finally, the bantam pilot was getting a mission commensurate with his desire.
Asamura may have been a talented pilot, but he was a difficult personality. A stickler for protocol, he angered easily when someone crossed his imagined boundaries. This keen sense of “correctness” meant he followed orders with exceptional dedication. It also meant he was rigid and unyielding. Whereas Takahashi was arrogant and critical, Asamura could be petty and vindictive. Their differing personalities would eventually clash. In the meantime, they focused on flying.
Seiran flight-testing was far enough along that by November 24, the plane was officially accepted by the IJN.36 Aircraft production was dealt a blow, however, when a December 7 earthquake shook Nagoya. The quake lasted five minutes, killed 1,000 people, and caused heavy damage. Though no Seiran were destroyed, their wing jigs were twisted like taffy, even though some metal pipes were 12 inches thick.37 Sen-toku personnel were rushed to the plant to assist in the cleanup.38 Meanwhile, production was brought to a standstill.
When the 631st was officially formed eight days later, no Seiran were available for the unit.* 39 They were still being tested. Asamura may have been proud to be assigned to the air group, but Takahashi wanted out of sub-borne airplanes. One reason was that he wouldn’t be flying in the relative safety of the Indian Ocean but deep in the heart of enemy territory. While Asamura was grateful to die for his country, Takahashi took a more jaded view. Since he considered defeat inevitable, little would be gained by his death in battle. In other words, being assigned to the 631st was “the worst possible news.”40
FINALLY, ON JANUARY 8, 1945, the I-401 was commissioned under the cloudy skies of Sasebo. Since the sub was top secret, few people attended the ceremony. When it was over, Nambu sailed the I-401 quietly out of the harbor.41
Although 60 percent of the I-400’s crew had limited experience aboard a sub,42 Nambu felt he had few greenhorns among his men.43 Forty percent of experienced submariners is low for a combat boat. It was certainly fewer than a U.S. sub was comfortable carrying.
Nambu didn’t linger in the waters off Kyushu.44 So many U.S. submarines were in the area that there w
as a saying: You could walk across their periscopes from Singapore to Japan without getting your feet wet.45 Nambu was right to be concerned. U.S. subs considered the sea lanes around Kyushu to be prime hunting ground, and the I-401 made a tempting target.46
Nambu quickly headed for the safe waters of the Inland Sea with Ariizumi onboard. They met up with the I-400 and I-13 near Kure, where they conducted dive and surface drills, practiced trimming the boat, and did underwater navigation exercises.47 After repeated practice, the I-401 could crash-dive to periscope depth in just under a minute—a significant achievement given the size of the boat but almost twice as long as the Segundo required.
ACCEPTANCE TRIALS FOR the underwater aircraft carriers were carried out separately from Seiran flight training.48 While Nambu’s sub underwent its shakedown period, the I-400 and I-13 assembled near Kure Naval Base to test the unloading, launching, and stowing of Seiran.49 It was the first important step in the marriage between submarine and aircraft, and success would lead to joint tactical training.
The catapult test was especially important. Meant to determine the maximum payload a Seiran could carry and still be launched from a sub, the test involved adding sand to a hollowed-out practice bomb, attaching it to a rack underneath the Seiran’s belly, and launching both from the sub. The bigger the bomb, the better the bang, but safety considerations played an important role. They discussed removing the plane’s floats, or reducing her fuel to accommodate the bomb load if the catapult tests failed. As it was, Takahashi successfully flew from the I-400’s deck carrying a 1,760-pound practice bomb, the heaviest ever launched from an IJN catapult.50
ARIIZUMI MADE HIS first appearance in the 631st’s command room on January 11, 1945. Many of the air group’s officers were nervous, having never met him before. Takahashi wasn’t one of them. He’d seen Ariizumi drunk in Penang and wasn’t the least bit intimidated. The same couldn’t be said for his fellow officers, though, who awaited their boss with trepidation.
Operation Storm: Japan's Top Secret Submarines and Its Plan to Change the Course of World War II Page 17