Operation Storm: Japan's Top Secret Submarines and Its Plan to Change the Course of World War II (14 page)

Water greatly amplifies sound, which means a depth charge explosion can deafen a crew if it is close enough. And nothing is more sickening than watching the hull flex inward every time a depth charge detonates. Many submariners swore that a detonation could convulse the hull as much as six inches. It wasn’t the kind of story you wanted to personally verify.

Though Hollywood loves depicting a sub being sunk by a single, well-placed depth charge, the truth was most subs were sunk by cumulative damage sustained over a prolonged attack. Another Hollywood fallacy shows a depth charge sending huge geysers of seawater cascading into the sky. Unless a sub was near the surface, this was the least effective means of attack because it meant the depth charge’s concussive pressure was vented into the air rather than against the sub’s hull. Nevertheless, depth-charge explosions were a nerve-wracking experience and submariners dreaded them.

The
Warrnambool
and
Kalgoorlie
tracked the
I-174
for two hours, dropping 36 depth charges in four separate patterns. Finally, when they lost contact and saw oil on the surface, they concluded the sub had been sunk.
¹⁹
The Royal Australian Navy was wrong, however. The
I-174
had sustained damage, but Nambu had escaped and soon resumed combat operations.
²⁰

Nambu’s success made him a hero to his crew. He’d attacked an escorted enemy convoy in broad daylight
²¹
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.

T
HE HISTORY OF
J
APANESE “MOLE” OPERATIONS BEGAN IN
A
UGUST
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 night
¹⁰
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.

N
AMBU
’
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 return 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 died
²⁴
(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.

N
AMBU 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.

W
HILE THE
S
IXTH
F
LEET 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 six
⁴
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.