On April 10 ten Seiran took to the air over Fukuyama to simulate attacking the city. After repeated diving from 16,000 feet, Takahashi’s air group finished for the day and headed back to base. Since a storm was coming, Takahashi landed in a river rather than the gulf, where the water was choppy. Two more Seiran landed without incident. When it came time for Second Lieutenant Ichiyoshi to put down, he ignored Takahashi’s example and chose the gulf instead. Takahashi held his breath as he watched Ichiyoshi’s plane make its approach.
Boy, that’s dangerous, he thought. I’ll have to reprimand him.
As he watched Ichiyoshi’s Seiran bounce across the waves, Takahashi grew increasingly concerned. When one of the plane’s pontoons broke off and the aircraft flipped over, he couldn’t stop himself from shouting, “You idiot!”
A rescue boat rushed to the scene, but Ichiyoshi’s head had smashed into the cockpit windshield, killing him instantly. His observer was luckier. Thrown clear of the plane, he survived the crash.23
It was the third accident and fifth fatality for the 631st. Though not unexpected, given the high-risk nature of their training, the casualties were beginning to add up.
AS IF EARTHQUAKES, aerial mines, aircraft accidents, and enemy fighters weren’t bad enough, the Sen-toku subs soon found themselves out of fuel. Vice Adm. Charles A. Lockwood, commander of the Pacific submarine force, knew Japan’s fuel was running low. His subs had sunk 76 oil tankers with just such a goal in mind.24 What Lockwood couldn’t have known, was just how little oil was left.
Normally, an I-boat would have enough fuel to spend three months searching for targets. But fuel was now so scarce, Japan’s few remaining subs had to take the most direct route to a shipping lane and wait for something to cross their path.25 The IJN’s fuel shortage was further compounded when the super-battleship Yamato drained the tanks at Kure’s Tokuyama storage depot in April.26 The Yamato was heading to Okinawa to repel the U.S. invasion. Even if she survived the sortie, she would have only enough fuel for a one-way trip.27 Some have speculated that the Yamato was sacrificed in order to preserve fuel for the I-401’s mission.28 There is no evidence for this claim. The IJN started the war with six million tons of oil,29 enough to last two years. But Tokuyama, despite being one of the largest oil facilities in the IJN,30 only had 2,000 tons left.31
The I-400 and I-401 each required 1,700 tons of fuel to complete their missions,32 and priority was traditionally given to the surface fleet. Attacking the Panama Canal might have been important, but Ariizumi had to compete with the rest of the navy for his fuel allotment. There just wasn’t enough to go around.
The 631st faced similar problems. So little aviation fuel was available that the Seiran squads barely had enough for training. Low in octane, the fuel had been blended with turpentine and alcohol to make it go farther, but it was such poor quality, the pilots jokingly called it “Marianas gas.”33 The IJN was aware of the problem and planned to use submarine tankers to import two million gallons of fuel from Singapore and Formosa. The I-402 fell prey to this initiative, along with seven I-class and four HA-class subs. Instead of being completed as an underwater aircraft carrier, the I-402 was converted into a giant underwater tanker, with a fuel capacity of 182,000 gallons.34
Given the fuel shortage, Ariizumi faced a difficult choice. Kure had only enough fuel for one I-400 sub. Without fuel there was no training, no mission, and no hope of staving off defeat. Unfortunately, the Combined Fleet could not give what it didn’t have. Ariizumi would have to go elsewhere.35
The only place where fuel could still be found in any appreciable quantity was at the IJN naval bases in China and Korea. And so Ariizumi decided to sail his flagship to the port of Dalian in Manchuria to get oil from the stocks located there.
It wasn’t going to be easy. To reach China, the I-401 would have to sail south through the Inland Sea to one of two exits, the Shimonoseki Strait on Japan’s west coast, which led to the Sea of Japan, or the Bungo Strait on Japan’s east coast, which led to the Pacific. Both exits were heavily mined, and each had its own set of problems. The Shimonoseki Strait was a ten-mile doglegged channel whose narrowest point was only 800 yards wide. It would be nearly impossible to thread it without encountering a mine. On the other hand, American subs were posted outside the Bungo Strait, just itching to sink any I-boat entering the Pacific.
Ariizumi had no alternative. If he didn’t try for China, he’d never get enough fuel to continue training, let alone embark on his mission. But if he braved the mine-infested waters, there was a good chance he’d never reach China. Ariizumi finally decided on the Shimonoseki route. Yes, it was heavily mined, and there was always the chance the U.S. Navy might attack in the Yellow Sea. Nevertheless, it was the shortest distance between Kure and Dalian. Additionally, the I-401 had a degaussing mechanism, six cables snaking their way the length of the outer hull. They not only prevented the sub from rusting, they helped shield it from mines by dampening its magnetic field. They would just have to risk it.
Since traveling on the surface was the fastest way to Dalian, Ariizumi had a wooden smokestack added to his flagship to disguise her identity.36 Given her size, the I-401 could easily pass for a surface ship. Whether the deception would save her from attack was debatable, but it certainly masked her aircraft-carrying secret.
The I-401 departed Kure on April 11.37 She had just left the harbor when a swift current ran her aground. Nambu dumped ballast and quickly refloated her,38 but it was an unlucky start. The next day the I-401 was again traveling on the surface. It was 8:50 in the morning, and they were off Hime Island in the Inland Sea. Nambu was on the bridge, and since they had only a short distance to go before reaching the entrance to Shimonoseki, he made it a point to warn his sonar operator to keep a sharp lookout.39
Both Ariizumi and Yata, the chief gunnery officer, were in the wardroom having coffee.40 A moment later both men felt an explosion lift the sub’s stern into the air. Ariizumi’s coffee cup hit the ceiling before spilling its contents.41 Moments later the crew began sealing the sub’s watertight doors.
In the split second it took Nambu to register the explosion, he knew they’d hit a mine. Was it survivable? Until the damage reports came in, he was at the mercy of his imagination. In the meantime, the sound of water gushing into the sub was not reassuring.42
CHAPTER 22
ATTACKING THE CANAL
THE I-401 WAS IN 160 FEET OF WATER WHEN A MAGNETIC MINE released its anchor and floated toward the surface.1 The ensuing explosion may have shaken the whole boat, but it was the stern that bore the brunt of the damage.
A white haze enveloped the aft deck as a churning mass of ocean boiled around the stern.2 Had the I-401 been traveling any slower, the mine would have hit amidships, possibly sinking her. As it was, the I-401’s twin propellers and their respective shafts were also vulnerable, as were her stern planes. A mine explosion in the stern could just as easily sink them.
Initial reports indicated that a fuel tank had been ruptured,3 and a Kingston valve (which regulated the flow of seawater into the ballast tanks) was damaged.4 It didn’t take long for Nambu to ascertain the I-401 would survive. Even so, she was in no condition to travel to China. Traveling with an oil leak was like laying down breadcrumbs for the enemy to follow. As for the gushing water, the explosion had ruptured a sake tub, sending its contents spouting into the sub.5 Everyone had a good laugh about that.6 It had been a close call though. All they could do now was limp back to Kure.
Unfortunately, Ariizumi was no closer to obtaining the fuel he required. With his flagship in need of repair, he had no choice. He had to send the I-400 in place of her. Kusaka’s sub was virtually identical to the I-401, save for a few cosmetic differences. She also had the same large fuel capacity, which meant she was a more logical choice than the smaller-capacity I-13 or I-14. The one thing the I-400 did have that the other subs in the Sen-toku fleet lacked was Cdr. Toshio Kusaka.
Kusaka was a highly skilled captain, as evidenced
by his commander title and three previous sub commands.7 He’d also recovered enough from the minor wounds he’d sustained during the Kure air raid to resume skippering his sub. Born in a small village on the island of Shikoku in June 1904, Kusaka had wanted to be a fighter pilot but was steered toward submarines because of his small stature.8 Like Nambu, he was an Etajima graduate. He had also been at Pearl Harbor, captaining the I-74. When Doolittle’s Raiders bombed Tokyo in April 1942, it was Kusaka’s sub that had been sent to intercept the USS Hornet (CV-8).
It’s likely Kusaka and Nambu knew each other before joining the Sen-toku squadron. Kusaka had turned command of the I-74 (later designated the I-174) over to Nambu in November 1942. Kusaka had also captained war patrols off the Australian coast and transported ammunition and supplies, just like Nambu. Although their résumés were similar, Kusaka was more experienced than Nambu, which is probably why he had his own command while Nambu had to captain under Ariizumi’s watchful eye.
Kusaka had also served in the Indian Ocean at roughly the same time as Ariizumi. He’d commanded the I-26 and sunk two tankers between December 1943 and March 1944. One of his most memorable missions involved landing Indian revolutionaries near Karachi to promote an uprising against the British. Though most of the nationalists were captured or killed, it was the kind of old-fashioned spy caper that only happened in novels.
Three days after Ariizumi massacred the SS Tjisalak’s crew, Kusaka followed suit, using the I-26’s deck guns to riddle the lifeboats of an American Liberty ship, the SS Richard Hovey.9 Kusaka killed eight survivors,* making him one of four SubRon 8 sub captains implicated in killing prisoners. By August 1944, Kusaka was named chief equipment officer for the I-400.
“Kusaka was the best captain anyone could ask for,” Lt. Kazuo Nishijima, the I-400’s chief navigator, noted.10 Since Nishijima was the sub’s second seniormost officer after Kusaka, it was no small compliment.
Kusaka’s many years of combat experience, combined with his unquestionable ability and good judgment, earned him the respect of his crew.11 Importantly, he radiated the same kind of confidence as the Segundo’s Captain Fulp. Not surprisingly, Kusaka’s crew would do anything for him.12
Dalian, located near Port Arthur on the Yellow Sea, was an important commercial port. When Russia lost its war with Japan, it had conceded Dalian in 1905. Since then, the IJN had made significant investments in the port, which was now home to a large stock of diesel fuel.
The I-400 left Kure for Dalian on April 14 disguised as a frigate.13 Barrels were placed on the catapult rails and covered with a canvas tarp, while dummy cannons and machine guns were added to complete the ruse.14 Kusaka navigated the Inland Sea at reduced speed to avoid triggering mines. As he approached Himejima, the island where the I-401 had nearly been lost, he encountered some good luck. Two Japanese merchant ships were also heading through the Shimonoseki Strait. Kusaka joined the middle of their single-file procession, using the lead vessel to shield his sub from any mines in his path.
As Kusaka followed the first ship into the narrow strait, the I-400 proceeded slowly on the surface. The channel was quiet save for the seagulls overhead, whose shrill cries sounded like a warning not to proceed. From his position on the bridge, Kusaka could see the red-bellied bottoms of capsized ships as the I-400 passed by. Those that had rolled over revealed the ugly puncture wound of a mine explosion against their hull. Other ships had simply settled on the canal floor, their bottoms ripped out by 1,200 pounds of high explosives. With their decks awash, and masts poking above the waves, Shimonoseki looked like a graveyard for ships.
Suddenly, the freighter ahead erupted in an explosion as a mine tore out its keel.† The ship was so close that the smoke pouring from her hold made Kusaka’s eyes water. Though he could see the ship’s crew jumping overboard, he could not stop to assist them. Everyone was on their own in a situation like this. The shore was not far away, and rescue stations had been established for just such an occasion. The explosion had been so violent though that many of the ship’s crew probably never made it above deck. It was a chilling reminder that the odds of survival were no more than a coin toss.
After Kusaka navigated past the expiring vessel, he found himself in the lead. Without a buffer, he worried the I-400 would be sunk next. As anyone who’s ever been trapped in a minefield knows, the anticipation of destruction is excruciating. Lookouts can scan the water all day, but they are unlikely to spot a mine beneath the waves. What’s more, sonar was useless in a narrow channel riddled with wrecks. Even so, Kusaka never considered turning back. The channel was too narrow, there was a ship following him, and Ariizumi would have condemned him. His only escape was forward.
To Kusaka’s surprise the ship behind him was next to hit a mine.15 After an enormous explosion, the freighter quickly filled with water. Kusaka must have felt that the spirit Ise watched over him that day, since the I-400 was the sole survivor of a three-ship convoy.
After successfully navigating the rest of the strait, the I-400 arrived in Dalian on April 20.16 Kusaka released his crew for shore leave, which included a Chinese banquet hosted by the Manchurian Railway, and the company of “comfort women” from Korea, China, and Japan.17 In the meantime, the I-400 took on 1,700 tons of fuel made from liquefied coal18 as well as a cargo of soybeans,19 iron,20 peanuts,21 and molybdenum.22 When Kusaka departed for Kure, the return trip proved uneventful.23
WHILE THE I-401 was undergoing repair, Ariizumi used the time to adopt what he hoped would be a game-changing technology. The device he wanted to use was called a snorkel, and the reason he wanted his flagship to have one was that he believed it would help her to remain hidden underwater longer.
The device was simple enough. Two pipes, one for air intake, the other for exhaust, were mounted on the periscope shears. Both pipes connected to the sub’s auxiliary engines, supplying oxygen and venting toxic gas. When the sub was at periscope depth, it could hydraulically raise its snorkel above the surface,24 and because each pipe had a self-sealing valve, water couldn’t flood in.
The small size of the pipes made them invisible to radar and difficult to spot at a distance. Radar itself was a game-changing innovation that put Sixth Fleet subs at a disadvantage. Since Japan adopted the technology late, Ariizumi was betting the snorkel could help level the playing field. Being able to use their auxiliary engines while submerged might give them just enough extra time to escape undetected.
Ariizumi’s hopes for the snorkel were not unreasonable. If the Sen-toku subs could remain hidden underwater a little bit longer, they could slip past the U.S. Navy to launch a surprise attack.25 Interestingly, American subs didn’t use snorkels. The U.S. Navy felt their cost, weight, space requirement, and reduction in engine performance outweighed any benefits.26 It didn’t hurt that the Pacific sub force was so strong, it had little reason to hide. U.S. subs wouldn’t adopt the technology until after the war. When they did, Portsmouth was the first shipyard to add them.27
After the I-400 returned to Kure, Ariizumi ordered his three other submarines outfitted with snorkels, making them one of the first Sixth Fleet subs thus equipped.28 Installation took most of May,29 but the lost time was worth it, especially if it created an advantage Ariizumi could exploit.
Next, the squadron commander called a meeting to brief the officers of SubRon 1 and the 631st air group on the Panama Canal attack. Held at Kure Naval Base on or about April 25,30 the meeting included among others: the 631st’s seniormost officer, Lt. Cdr. Masayoshi Fukunaga; two of its most senior pilots, Asamura and Takahashi; and SubRon 1’s four sub captains: Nambu, Kusaka, Shimizu, and Ohashi. Given the importance of the mission, representatives from the Naval General Staff and Sixth Fleet also attended, including Commanders Shojiro Iura and Yasuo Fujimori.31
The meeting began promptly at 9:00 A.M.32 Chairs had been set up in the briefing room, and a large board diagrammed the route to Panama.33 Ariizumi arrived, looking tan from all the time he’d spent on the I-401’s bridge. When all rele
vant personnel had gathered, the 631st’s XO, Fukunaga, called the meeting to order.
“Based on the latest map exercise,” he said, “I would like to explain SubRon 1’s strategic plan and decide our training goals going forward.”34
The plan was as easy to articulate as it was difficult to carry out. First, the Sen-toku squadron, comprising the I-400, I-401, I-13, and I-14, would travel the same course as Nagumo’s carriers had on their way to Pearl Harbor.35 After passing north of Hawaii, Ariizumi’s subs would then head southeast until they reached the coast of Ecuador.‡ When they were 100 miles off Ecuador, the subs (separated by 50 miles) would surface and launch their ten Seiran aircraft at 3:00 A.M.36 To accommodate the maximum bomb load, the Seiran would be stripped of their floats. Once launched, the aircraft would rendezvous, then fly northeast across the top of South America, passing over Colombia. To avoid radar contact, they would fly at low altitude. Once they reached the Caribbean, they would double back and head toward the Atlantic entrance to the canal.
Ariizumi was counting on the destructive force of ten Seiran payloads to destroy the lock gates. Given the fact that Gatun was the largest manmade lake in the world, he had a good chance for success if his planes got through. If for any reason the Seiran didn’t completely destroy the upper lock gates, the massive outward pressure of the lake would finish the job.
After the Seiran destroyed the gates, they were to rendezvous with their mother subs in the Gulf of Panama. Ditching their planes in the ocean, the aircrews would swim to their respective subs, climb on board, and return home to Japan.
Several important questions remained, however. One of the biggest was which ordnance to use to destroy the lock gates. Fujimori’s team at the Naval General Staff had researched this question and come to the conclusion that a combination of torpedoes and bombs would be most effective,37 but more research was required.
Operation Storm: Japan's Top Secret Submarines and Its Plan to Change the Course of World War II Page 21