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

by John Geoghegan

  Nambu’s success made him a hero to his crew. He’d attacked an escorted enemy convoy in broad daylight21 and gotten significant results. In fact, Nambu’s attack proved to be the most successful by a single Japanese submarine off Australia’s east coast.22 It also turned out to be the last two ships sunk in the region by a Japanese sub.23

  As Japan’s defense perimeter continued to weaken, I-boats were recalled to defend the South Pacific. This meant fewer combat subs were available to sink merchant ships off Australia. The I-174’s run was cut short for this reason. But Nambu wasn’t just being recalled to defend the empire—he was being given the most despised assignment in the Sixth Fleet sub force.

  Nambu was becoming a mole.

  * Nambu remembers it as a large, armed commercial vessel rather than a U.S. Army transport, but Allied records are more accurate in this instance; the I-174 was probably too far away to accurately identify the type of ship.

  † Though Nambu believed he’d hit the ship, there is no Allied record confirming a ship was attacked on this date at this location.

  ‡ Allied naval records show that Nambu fired upon the American Liberty ship SS John Bartram. All four torpedoes missed.

  § The LST-469, though damaged, remained afloat and was eventually towed back to Sydney. It belonged to MacArthur’s newly formed Seventh Amphibious Force, which was short of ships. Loss of the vessel forced the last-minute elimination of troops and cargo from the assault convoy destined for MacArthur’s first amphibious operation, the occupation of Kiriwina and Woodlark islands. See David Stevens, “The Naval Campaigns for New Guinea,” Journal of the Australian War Memorial, n.d., http://​www.​awm.​gov.​au/​journal/​j34/​stevens.​asp.

  CHAPTER 10

  NAMBU BECOMES A MOLE

  THE HISTORY OF JAPANESE “MOLE” OPERATIONS BEGAN IN AUGUST 1942, when Admiral Yamamoto first ordered high-speed destroyers to ferry supplies to Japanese troops on Guadalcanal. Americans nicknamed the supply runs “The Tokyo Express” due to their speed and punctuality. Japanese destroyer captains had a different name for them. They called them the “Mouse System” because the enemy were like cats always waiting to pounce.1 Eventually, the Allies so dominated the South Pacific that the Imperial Japanese Navy could no longer get supplies through via destroyers. That’s when Yamamoto turned to Sixth Fleet submarines to take up the slack.

  Underwater cargo duty was the most despised assignment in the Sixth Fleet, and Nambu hated it.

  “Subs were meant to attack,” he protested, “not to be deployed as cargo carriers.”2

  Disparagingly referred to as moruga, or “mole” ops,3 it wasn’t the kind of duty a combat sub captain took pleasure in performing. Though most submariners appreciated that they were on a humanitarian mission, turning combat subs into cargo ships—a purpose for which they were never intended nor especially well suited—created complications. One reason Nambu hated it so much was that transporting cargo was just as dangerous as combat ops without the satisfaction of attacking the enemy. The goal was to deliver supplies, which meant they had to remain hidden to successfully complete their task. Since a sub’s crew is motivated by sinking ships, not ducking them, Nambu felt moruga ops hurt morale.4 Of course, he did his best to maintain his crews’ spirits, but the very nature of supply missions undermined his efforts.

  U.S. Navy cryptographers presented another danger. Sixth Fleet radio traffic was being read by the Allies on a regular basis.5 Consequently, U.S. naval forces knew a Japanese sub’s destination as well as its arrival date and time. This significantly improved Allied antisub efforts, and Sixth Fleet losses increased commensurately. Just as bomber crews in England didn’t expect to survive a set number of missions, Sixth Fleet submariners felt each moruga deployment would be their last. Even the soundest of men could crack under the pressure.

  Worst of all, since every bit of space was needed for supplies,6 combat subs had their torpedoes removed and their tubes used for storage.7 Even a sub’s deck guns were stripped to help offset the increase in cargo weight. This eliminated a sub’s offensive capability, further depressing her crew.8

  Despite the drawbacks, moruga ops would benefit the future captain of the I-401 in ways he couldn’t foresee. Stealthily transporting high-value cargo to a well-defended location was ideal training. Instead of carrying food and medicine, he’d be transporting three special attack planes to launch against the Panama Canal, but the skill set was the same. And though Nambu would continue yearning to attack the enemy at every opportunity, he would also learn the discipline necessary to carry out his mission.

  By January 1943, as many as 20 subs were reassigned from combat to supply operations.9 Typically, a sub would surface on a moonless night10 and pass her cargo by hand to a waiting motorboat.11 Allied naval dominance soon made it too dangerous though for subs to surface, and new methods had to be employed. First they tried ejecting supplies through the torpedo tubes, but cargo was damaged.12 Next, supplies were secured to a sub’s deck in rubber bags with just enough air sealed inside to allow them to float.13 When the sub reached its destination, the bags were released and sprung to the surface, where marooned troops retrieved them.14 Unfortunately, bags were occasionally contaminated by seawater or burst before reaching the surface. From January 1943 on, steel drums were used,15 but problems remained. Storage drums were subject to tremendous variations in sea pressure. More than one supply mission arrived at its destination only to find its cargo had been lost along the way. Given the risks involved, it was a dispiriting lesson.

  Rice and wheat were the chief supplies, though canned biscuits, salt, soy sauce, bean paste, plums, and dried bonito fish were also carried. Mail from home was especially appreciated, as were clothes, mosquito nets, medicine, small arms, and ammunition.16

  One sub carried enough supplies to support 30,000 men for two days,17 which sounds like a lot. It wasn’t though, given how difficult it was for moruga subs to complete their mission. Despite the mole operations, Japanese troops were continually at risk of starvation. The use of combat subs to resupply them only shows how desperate the war had become.

  NAMBU’S FIRST MISSION was transporting supplies from Rabaul on one side of New Guinea, to Lae on the other.18 On August 17, 1943, he loaded food, ammunition, and fresh troops into his sub before departing. The troops at Lae were so hungry, they were eating grass. Nevertheless, every time an enemy ship passed overhead Nambu resented not being able to attack.19 Sixth Fleet’s commander in chief had made it clear that supply operations were to succeed no matter what,20 which meant Nambu couldn’t sink the enemy. No wonder he hated the job.

  Three days later Nambu’s crew offloaded supplies, replacing them with wounded soldiers for the return trip. The submarine was already so cramped that adding 40 casualties among a tightly packed crew made life miserable for everyone.21 The moans of dying men frayed the crew’s nerves and the smell was terrible. Somehow they returned to Rabaul without incident.

  There were two more runs like this, the third being the worst. A B-24 dropped four bombs near them followed by an enemy sub sneaking up and firing three torpedoes. If Nambu hadn’t reacted quickly, it would have spelled disaster. As it was, they barely escaped.

  Nambu returned to Rabaul without completing the mission. He informed his command that it was impossible to deliver supplies when surrounded by the enemy. It wasn’t that Nambu feared dying—he protested because he hated the thought of losing his crew in such a wasteful effort. The response was predictable. He was told to “force it.”22

  Nambu and his crew never got enough rest, partly because so many subs had been lost. Usually, they had only a few days in port before they were sent back out again. The loss of subs also meant a reduction in crew replacements. It was only a matter of time before an overextended crewman made a fatal mistake.

  Nambu’s fourth supply mission fared no better. Four times they were spotted by enemy planes, and four times they were forced under. They eventually made it to Lae, but on the re
turn trip they faced a four-hour depth-charge attack, during which one of the soldiers they’d evacuated died of heatstroke. This left Nambu frustrated and depressed.

  “I rely too much on my Japanese spirit,” he wrote in his diary. “It is not enough. The enemy goes about freely … while we don’t have a single torpedo … Do our countrymen know about our toils? We cannot win.”23

  Though a realistic assessment, it was uncharacteristically downbeat for Nambu. But the I-174’s captain had good reason to be depressed. He was notified in October that his sister, the only surviving member of his family, had died24 (most likely of tuberculosis, which was rampant). Then Lae fell, despite his efforts to keep it resupplied. Finally, on November 20, 1943, Nambu received word that Masamichi, his firstborn son, had drowned. He must have felt his world was collapsing.

  NAMBU KNEW LITTLE about his son’s death, but what he did learn was crushing. His wife, Yukiko, had been invited on an outing to pick mikan, a type of orange, on the island of Kamakari. Fruit was a particular treat given wartime shortages, and Yukiko spent a pleasant afternoon wandering the orchard with her two sons Masamichi, now three years old, and infant Nobutaka. The navy wives gossiped while their children played among the orange trees. When it came time to return, two boats waited to take the families across the bay. The father of another family offered to take Masamichi, Nambu’s oldest son, in a separate boat so Yukiko could focus her attention on the newborn. Yukiko resisted though. Her mother’s instinct was to keep both children with her. When the man insisted, she gave in.

  As she handed over her oldest boy to the helpful gentleman, she implored, “Please take care of my son.”

  “Don’t worry. I will,” he replied.

  The boat carrying Yukiko and her baby arrived at the Kure beach first. But as the second boat approached, it overturned, casting Masamichi into the water. Nambu’s wife immediately rushed to rescue him, but just as she reached for his tiny hand, a large wave swept him from her grasp.

  It was a devastating blow. Nambu loved his family, but a sub captain can’t show grief in front of his crew. As a result, he did his best to suppress his feelings. It was only through sheer will that he managed to function.

  Finally, after completing seven supply missions, Nambu was promoted. He’d successfully delivered a total of 310 tons of matériel to the battlefield. Despite seven missions though, the I-174 supplied no more cargo than one merchant ship could carry in a single voyage.25 This problem would be partially addressed when the Sixth Fleet launched a new class of cargo subs later in the year. In the meantime, combat subs continued filling the gap.

  CHAPTER 11

  SEIRAN TAKES FLIGHT

  WHILE THE SIXTH FLEET STRUGGLED WITH STRATEGIC ISSUES, the I-400 construction program forged ahead. Production of the I-403 began at Kawasaki Heavy Industries in Kobe on September 29, 1943;1 keel laying for the I-402 followed in Sasebo a few days later;2 and construction on the fifth sub, the I-404, was set for February 1944.3 This means at least five I-400 subs and possibly six4 were in varying stages of production by the end of 1943. When the I-13 and I-14 were included, a third of the squadron was under construction.

  Meanwhile, the first test flight of Aichi’s special attack plane was held on November 8 that same year.5 Lt. Cdr. Tadashi Funada was her chief test pilot. A highly respected member of the Flight Technology Test Group at Yokosuka, Funada was probably the foremost seaplane pilot in the Imperial Japanese Navy. And because of his extensive experience, he was as much involved in the plane’s design as in her flight testing.

  Aichi’s special attack plane must have created quite a stir when she first rolled out of her top secret assembly building.6 For one thing, experimental aircraft were painted bright orange,7 and the plane was so big, her cockpit stood more than 15 feet off the ground. She was the largest aircraft ever carried by a submarine.

  Aichi’s M6A1 was designed to do two mutually exclusive things: dive steeply to drop a bomb or come in low to launch a torpedo.8 The first type of attack required “dive brakes,” which slowed a plane enough that it didn’t tear apart while diving. A torpedo attack, however, required a plane to fly low, straight, and fast. Each attack required different wing flap configurations and plenty of practice to master. In other words, Aichi’s special attack plane was not for beginners. Then again, Funada was hardly a beginner.

  It was a cold, gray day when Funada climbed into the cockpit. As he taxied down the nearby river, he looked forward to how the prototype would handle. But when he began climbing over Ise Bay,9 he quickly realized something was wrong. The elevator controls on the plane’s horizontal tail stabilizer, which controlled the plane’s angle of climb or descent, weren’t working.10 A plane losing elevator responsiveness is akin to a car losing its steering. That’s why Funada knew he had to make an emergency landing, and in a hurry.

  The only way Funada could get the plane to descend was to throttle back her engine. As the plane’s speed decreased, she began dropping through the snow-laden clouds. Careful not to stall, Funada became conscious of another problem as he made his approach. Floatplanes are notoriously difficult to land. They tend to be nose heavy, and if pilots aren’t careful, they can easily flip over. Fortunately, Aichi had designed the aircraft to be less nose heavy than other seaplanes. As Funada eased back on the throttle, he felt the plane make contact with the waves. He had barely made it back alive.11

  It might have been a successful landing, but it wasn’t a successful test flight. The ailerons had to be redesigned,12 one of several aerodynamic problems that plagued the prototype.* 13 Another of the plane’s “x factors” was its floats. They were so large, the design team worried they’d create too much drag. The plane’s wing area was increased to provide more lift,14 but there were also problems with the plane’s vertical stabilizer, which had to be lengthened to improve handling.15 Unfortunately, the increased tail height meant the aircraft no longer fit inside the sub’s low-ceilinged hangar. At first Toshio Ozaki, the plane’s chief designer, considered making the tail assembly detachable.16 But anything that had to be attached, like floats, required more time to assemble and launch the plane. Ozaki fixed the problem by hinging the vertical stabilizer’s tip so it could be folded down, allowing the aircraft to fit inside the hangar. The plane’s horizontal stabilizers were also hinged for similar reasons.17 It was an ingenious if simple solution, leaving the floats the only detachable element.

  One of the unusual characteristics of the attack plane was its water-cooled engine. Most Japanese seaplanes relied upon an air-cooled engine, but a water-cooled engine offered several benefits. First, it enabled the plane to warm up inside the sub. This not only reduced the plane’s launch time—it minimized the time a sub had to be surfaced. Given that every minute increased the sub’s risk of discovery, this was an important improvement. A water-cooled engine also lowered the aircraft’s nose enough that it could fit inside the hangar. Additionally, it provided the necessary clearance between the propeller and the overly long torpedo the Seiran would have to carry, as well as better visibility from the cockpit,18 an improvement Sen-toku pilots would come to appreciate.

  The water-cooled engine was licensed from Germany’s Daimler-Benz, further refined by Japanese designers, and named Atsuta, after a local Nagoya shrine. Based on Daimler’s DB 601A engine, the Atsuta engine had 12 cylinders and delivered 1,400 horsepower at takeoff.19 The Atsuta engine was not without problems, however. For one, lack of materials and poor metallurgy meant they required more maintenance than air-cooled engines. They also had a tendency to leak oil. As a result, it took a while before mechanics had the engine functioning properly, and even then it suffered from occasional problems. For now though, wing flaps, not the engine, were the main concern.

  Aichi evaluated the special attack bomber against its own Suisei, since the plane was a naval dive-bomber too. Tests showed they had a similar rate of climb, but the combined weight and drag of the M6A1’s floats reduced its cruising speed. Without floats, the plane
was specced to achieve a maximum air speed of 345 mph, more than the comparable Curtiss SB2C Helldiver. With floats, however, the plane’s performance was only 295 mph, comparable to the Helldiver’s top speed but still a substantial decline. The attack bomber’s range was almost a third less than the Suisei. Fortunately, since the plane would be launched from a submarine close to shore, range was less important.20

  Despite problems with the maiden flight, the navy was satisfied enough to order 44 aircraft.21 Given the importance of the mission, however, the plane needed a proper name. The Imperial Japanese Navy didn’t always use utilitarian names when it came to its aircraft. Aichi’s Suisei means “comet” in Japanese; Saiun, a reconnaissance aircraft, means “painted cloud.” So, when Funada was asked by the Naval Air Command to come up with an appropriate moniker, he wanted something that did justice to the aircraft’s special mission. He named it Seiran.

  Composed of two kanji characters, Seiran can be translated as “storm from a clear sky.” The name was inspired by an eighteenth-century woodblock print by Hiroshige.22 Called Seiran of Awazu, the print shows the village of Awazu after a storm with mist rising from a nearby mountain. Funada hoped that the Seiran special attack planes would surprise the enemy by suddenly appearing “like a ninja out of the fog.”23 Therefore the name was not only inspiring because of its glamour, it accurately captured its purpose as well.

  As far as Japan was concerned, the United States had turned a blind eye toward her aspirations for nearly 40 years. When America wasn’t ignorning, belittling, or discriminating against Japan, she was seeking to hem her in. First the United States, Britain, Italy, and France had refused Japan a comparable-sized navy to limit her potential as a strategic rival; later the United States embargoed the precious oil that the IJN needed to function.