SHIP SIZE COMPARISON CHART
IMPERIAL JAPANESE NAVY I-401 SUBMARINE - 400 FEET
IMPERIAL JAPANESE NAVY I-14 SUBMARINE - 373 FEET
U.S. NAVY FLETCHER-CLASS DESTROYER - 376 FEET
U.S. NAVY BALAO-CLASS SUBMARINE - 312 FEET
PART IV
THE MISSION
CHAPTER 17
NAMBU AND THE I-401
THE I-8 DOCKED AT YOKOSUKA NAVAL BASE ON OCTOBER 9, 1944.1 The Sen-toku squadron was in the final stages of construction when Ariizumi left his sub for the last time and hurried to Tokyo to be briefed by Yasuo Fujimori of the Naval General Staff.2
Ariizumi knew the I-400 subs were a career-making assignment. Many in the Imperial Japanese Navy considered attacking the Panama Canal to be as important as the latest suicide weapon, a human-guided torpedo called a kaiten. Executed properly, the Sen-toku attack might help Japan fend off defeat. Ariizumi felt honored to be given responsibility for such an important mission.
The I-400 subs were to be organized into Submarine Squadron 1 (SubRon 1) and based in Kure. SubRon 1 was the only Sixth Fleet squadron consisting entirely of subs—no surface flagship or tender would be needed for their mission. Initially, SubRon 1 would consist of four subs: the I-400 and I-401 and the I-13 and I-14. If all went well, three of the four subs would launch before the end of the year, with the I-14 following shortly thereafter.
As Fujimori described it, the amount of men and matériel allocated to the program was nothing short of incredible. Nearly 600 submariners would man the four subs. The I-400 and I-401 alone accounted for more than half that number. This didn’t include their Seiran pilots and observers, or the maintenance technicians, ground crew, and armorers needed for land and sea assignment. In other words, the underwater aircraft carriers and their support personnel totaled nearly 1,000, almost as many men as were found in the average Japanese infantry battalion.
The amount of manpower necessary to construct the Sen-toku squadron was equally enormous. So great were the resources required to build four submarines that three separate naval yards were employed, both military and civilian. Supplying steel created such a drain on Japan’s shipbuilding program that naval higher-ups constantly complained about the shortage.
And that wasn’t all. There were four additional subs in various stages of completion: the I-402 would be ready by July 1945, and the I-404 (the next furthest along) would follow later in the year. As for the I-403 and I-405, the former was in the early stages of construction, while the latter hadn’t been built yet. As for the 12 remaining boats I-406 through I-417, they were paper subs only. They’d never got past the planning stage.
The resources devoted to the Sen-toku subs were astonishing given the damage the Japanese war machine had sustained. It signaled just how strongly the NGS believed in the mission.3 Japan’s defense perimeter may have been crumbling, but if the subs could destroy the Panama Canal, thereby stopping war matériel and reinforcements, they just might prevent compliance with the Allied demand for unconditional surrender.
Ariizumi was glad to hear that his subs were nearing completion, but he must have felt concern as to whether there would be enough time both for sea trials and for a full training schedule. The earliest he could start would be around the New Year. Given how poorly the war was going, his squadron would have to rush to get ready.
After meeting with Fujimori, Ariizumi went to Shizuoka to spend a few days with his wife, Matsu, and their five children.4 It’s reasonable to assume he was glad to see them after such a long absence. Ariizumi may have been a war criminal, but he still loved his family. Not much is known about this visit except that he drank heavily during his stay.5 Whether it was to relieve the stress of the Indian Ocean massacres, to celebrate his new appointment, or just because he liked to drink, we can’t know for sure.
Ariizumi could be touchy, though. On a previous home visit, Matsu had served grilled sea bream the night before his sub was to leave. When Ariizumi ate only the bottom portion, she made the mistake of serving him the remainder for breakfast. When Ariizumi saw what she’d done, he erupted.
“I’m about to go on a boat!” he shouted, throwing his plate on the floor. “It’s bad luck to serve fish with no bottom!”6
Meanwhile work continued on the I-400 subs.
LESS THAN A month later, Nambu arrived at the Sixth Fleet Submarine Base in Sasebo. It was November 1, 1944, and a chilly wind blew off Mount Eboshi.7 Sasebo was a Pacific-facing port located on Kyushu, Japan’s southernmost island. Nambu’s experience captaining mole operations would prove useful in commanding the I-401. Instead of transporting food to remote islands, he’d be carrying three special attack planes to bomb the Panama Canal. It was definitely a step up. Not every sub captain had the discipline necessary to hide from the enemy. Nambu might have thought it a pathetic skill, but he soon learned just how handy it could be.
As Nambu strode across the naval yard, sparks rained down in a hellish waterfall while the pounding of hammers assaulted his ears.8 When he finally saw the I-401, he was shocked—nothing had prepared him for her overwhelming size. The boat was so huge, you could easily stack one of his former subs on her deck.9 And that wasn’t all. The I-401 was so secret that many of the guards didn’t know her true identity.10
A World War II sub was a lot more complicated than it looked. It wasn’t just a single hollow tube with a conning tower on top—it was three separate components welded together. The largest component was the sub’s pressure hull, which contained her habitable spaces such as the engines and control room. Next came her ballast and fuel tanks, which wrapped around the outside of the hull. These were filled with seawater, air, or fuel depending on the need. The third element was the sub’s superstructure, which sat atop the pressure hull. On the I-401, the superstructure supported the sub’s teak decking and was semipermeable to allow water (or air) to flow underneath; that’s why, when a submarine submerged, water could be seen spouting into the air. There was essentially nothing between a sub’s pressure hull and her deck except emptiness.
TOPSIDE
BRIDGE The next thing Nambu would have noticed was the I-401’s sail, also called a fairwater, sitting atop her hull like a castle turret. It was offset from the sub’s centerline nearly seven feet to port,* 11 to compensate for the weight of the aircraft hangar.12 Wrapped around the top of the sail was the bridge, the preferred location for surface attacks. It was a spartan affair, open to the elements, that could be used only when the sub was above water. The bridge was like an oversize crow’s nest. It contained five 20X pressure-proof binoculars;13 a repeater compass; a set of collision, dive, and battle station alarms; and a single Type 9614 25mm antiaircraft gun mounted on her aft section.15 When the dive alarm sounded, as many as eight officers and lookouts had to clear the deck in under a minute. Jumping through the narrow bridge hatch, they slid 25 feet down a ladder,16 like firemen down a pole. Less-experienced submariners burned their hands on the long slide down.17 At least there was a three-foot-thick canvas hassock to absorb their landing at the bottom.18 Occasionally a crewman lost his grip and plunged down the ladder, taking everyone with him.19 In that case not even a hassock could cushion their fall.
The sub’s two periscopes (attack and high angle) towered above the bridge, along with various radar and radio antennas. Additionally, there was a watch station on the air search radar column.20 The added height enabled a lookout to see farther than at deck level. This was important because a sub sat so low in the water, it couldn’t see the horizon 12 miles away. The I-401’s extraordinary height made this less of a problem, every foot helped. Of course, most subs lurked at periscope depth waiting for a ship to pass. Nevertheless, lookouts were crucial when the sub was on the surface, especially for spotting aircraft or smoke from an enemy ship’s stack. The I-401 may have had the latest surface and air radar, but no captain relied on it 100 percent. Sub lookouts were as important during World War II as they had been during the glory days of sail.
&
nbsp; GUN DECK Just beneath the bridge was the 100-foot-long gun deck. Sitting on the roof of the aircraft hangar, it was exaggeratingly described as a promenade worthy of the Queen Mary.21 Three waterproof triple-mount AA guns took up most of the area, one forward and two aft. Each gun required two men to operate and had its own ammunition scuttle. A pointer controlled windage from the left seat, while a trainer controlled elevation from the right.22 The target was framed in an open-ring gunsight, and the pointer fired the weapon by operating a foot pedal. Since each gun spat 220 rounds per minute and a single 25mm shell weighed five and a half pounds, they were a healthy defense against aircraft.23
Gun crews liked fighting it out on the surface: looking your enemy in the eye while doing something about it was preferable to waiting for the explosion of a torpedo. One problem with surface fighting, however, was that the motion of the sea made it difficult to fire accurately. Additionally, a single hit from an enemy shell could easily hole a conning tower, rendering a sub unable to submerge. Since a submarine’s true purpose is to destroy its enemies with a torpedo, most sub captains preferred a quick dive to a surface shoot-out, Hollywood movies not withstanding.
DECK The most obvious feature on the I-401’s deck was the 102-foot-long aircraft hangar.24 Stretching over a quarter of the sub’s length, the hangar was only a few inches shy of 12 feet in diameter25 and was capped by a massive cone-shaped door. The hangar was ribbed like a whale inside, and there were racks for spare parts, maintenance tools,26 and one set of Seiran pontoons. The hangar was so large, it presented a serious risk if flooded. A two-inch rubber gasket kept the door watertight, but there was always a chance the enemy might hole the hangar. In that case, the sub could release 220 tons of fuel to offset the lost buoyancy.27 Britain’s M-2 had taught the Japanese well.
CATAPULT AND CRANE The I-401’s catapult was custom built and, at 85 feet, 4 inches in length,28 longer than any catapult in the IJN. It was also the most powerful catapult the Japanese built during World War II.29 Using compressed air, it could launch a four-ton plane every four minutes at a speed of six knots.30 Catapult rails extended from inside the hangar and ran the length of the foredeck. As they approached the bow there was a three-degree incline to help give the airplane lift. There was also a collapsible crane located on the port side of the foredeck just in front of the hangar door.† When not in use, the crane lay flush with the deck.
ADDITIONAL DECK ARMAMENT In addition to the bridge’s defensive armament, the I-401 carried a Type 11 140mm gun on her after deck. The largest submarine gun in use, it was the same type as found on the battleship Nagato. Better described as a cannon than a deck gun, it was capable of firing an 84-pound projectile 16,400 yards at 2,789 feet per second.31 After the Seiran and Type 95 torpedoes, the I-401’s deck gun was its most dangerous weapon.
HATCHES Nambu’s sub had seven deck hatches, which granted access to important areas like the torpedo and engine rooms.32 Twenty-five inches in diameter, they were a comfortable fit for the Japanese.33 Each hatch, plus the sub’s two main induction valves and hangar door, was wired to a board in the control room that indicated whether they were open or shut. You never knew when the sub might need to dive in a hurry, so close attention was paid to this board to avoid accidental flooding. Occasionally, when the sub was cruising on the surface, a high wave swept over the main induction valve, causing a fluctuation in the boat’s internal pressure. When that happened, ears would pop and the engines would backfire, filling the sub with fumes. In addition to feeding the diesel engines with oxygen, the main induction provided battery and hull ventilation as well as some of the only fresh air the crew ever breathed. Everyone knew when the main induction was open because fresh oxygen (as good as sunshine) filled the boat.
STEALTH COATINGS Being the largest sub in the world had its drawbacks. One of them was a huge radar signature. To compensate, the sub’s sail was indented at its base, to reflect radar waves back into the sea. In case this wasn’t enough, the I-401 had two anechoic coatings on its hull, one above the waterline, the other below.34 According to Japanese navy personnel, the coating above the water absorbed radar waves, while the coating below the water was for “sound [echo ranging] protection.”35 Though the ability to fool sonar is questionable, there is some indication that the below-the-line coating helped dampen any sound emanating from the sub.36 This helped the sub avoid detection from anyone listening for her with a hydrophone. The coatings were black, lumpy, and easily abraded. They also reduced the I-401’s speed by a knot.37 If anyone questioned their efficacy, Nambu wasn’t one of them. Anything that increased his sub’s stealth factor was welcome, especially since the Panama Canal was so heavily guarded.
INTERIOR
It’s impossible to get lost aboard a submarine—all compartments are on the same horizontal axis, save the conning tower, and each compartment is sequential, one leading to the other. This means only a fool can’t find his way. But the I-401 easily made fools out of newcomers.
The first thing Nambu would have found confusing is that instead of each compartment having only two hatches, one leading forward and the other aft, four of the sub’s eight compartments had an additional hatch in the hull, leading into what appeared to be a second sub running alongside.38 This gave the impression that the I-401 was two subs welded together, with hatches connecting the starboard and port halves. There was an important reason for this twin hull configuration: it provided a more stable launch platform for three fully loaded attack planes. Still, two interconnected subs lying side by side would have disoriented Nambu, just as it would any submariner who was used to moving only forward or aft. Port or starboard had never been an option until now.
NO. 1 COMPARTMENT: TORPEDO ROOM The I-401’s torpedo room was located in the bow compartment. Most submarines have only one forward torpedo room, while the I-401 boasted two, one stacked on top of the other in a duplex arrangement. It was an unprecedented configuration for a World War II sub and immensely gratifying for any captain eager to sink ships.
A typical Balao-class sub carried six bow tubes, while the I-401 had eight, four in the lower compartment and four in the upper.39 Though a Balao sub also had four tubes in her stern while the I-401 had none, and carried 24 torpedoes to the I-401’s 20, no convoy or antisub patrol relished a sub that could launch eight of the war’s best torpedoes nearly all at once.
In truth, U.S. subs were at a disadvantage when it came to torpedoes though this would change as the war progressed. The Mark 14 was most accurate when fired from less than a mile away.40 As Japanese naval tactics improved, this became increasingly difficult, forcing U.S. subs to launch from a greater distance. Japanese subs faced no such hindrance. Their Type 95 torpedoes had a range of five to seven miles.41 It was like bringing a lance to a knife fight.
Each of the I-401’s torpedo tubes had two sets of doors, an inner set for loading and an outer set for exiting. The inner doors were strong enough to withstand the crushing force of the sea, and neither door could be opened at the same time, to prevent flooding. Spare torpedoes sat on racks just behind the loaded tubes and took up so much room, the crew slept on top of the ordnance.42
One detail Hollywood movies rarely got right was the sound a torpedo made exiting a sub. In the case of the I-401, a hissing of compressed air, followed by water flowing back into the tube, could be heard, though only in the torpedo room, since the compartment’s watertight doors were shut during battle. Japanese torpedoes were quieter than their noisy American counterparts, but a slight shudder could still be felt in the torpedo room whenever a “fish” launched.
NO. 2 AND 3 COMPARTMENTS (STARBOARD): FORWARD CREW BERTHING Directly aft of the torpedo room was the first of three crew compartments for enlisted men. The I-401 carried 174 crew and 21 officers,43 though the total number exceeded 200 once pilots and aircraft technicians were counted.‡ There were never enough berths for enlisted men. Officers and CPOs may have merited their own bunk, but third-class ratings slept wherever they found space,44
including on rice sacks.
The two forward crew compartments extended aft for nearly a quarter of the sub’s starboard side. Each compartment had a three-tiered bunk configuration similar to the Segundo. Despite the I-401’s size, however, conditions were just as cramped, with one important difference: Nambu’s sub carried almost three times as many men.
Each bunk hung suspended on chains and could be folded up as necessary.45 The crew’s gear was stored in floor lockers beneath the bottommost bunk.46 “Hot bunking,” or sharing a bed, was also common: when one man was on duty, another man slept in his bunk, and vice versa. Beds were often used as dining tables,47 and the forward crew quarters also had a section for toilets, or heads. The facilities were standard squat-style openings connected to a sanitary tank. Heavy usage and excretory inaccuracy caused by rough seas guaranteed that no one lingered.48 Some sub captains allowed their crew an occasional shower,49 but fresh water was in such short supply that bathing was the first luxury dispensed with once war commenced. Officers were limited to one cup of water per day for washing.50 Some used sake to wipe themselves down,51 though it didn’t help much since officers were limited to a single hand towel.52
NO. 2, 3, 4 COMPARTMENTS (PORT): OFFICERS’ QUARTERS AND WARDROOM On the port side of the no. 2 compartment was the officers’ galley. Some captains enjoyed special meals, but Nambu tended to waive this privilege.53 There was also berthing for six warrant officers and space for the hydrophone room. Sound is the most important sense a sub can have below periscope depth. It enables her to locate an enemy or, if she is too noisy, betrays her own position. Sound heads located outside the sub’s hull picked up underwater noise and relayed it to the hydrophone operator. The sea might have been noisy, but an experienced sound man could read it like a book. He could tell the difference between snapping shrimp and the click of a depth-charge detonator. He could even tell whether a ship was approaching or receding, as well as what type it was.
Operation Storm: Japan's Top Secret Submarines and Its Plan to Change the Course of World War II Page 15