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

by John Geoghegan

  The officer’s wardroom was on the port side, opposite the crew’s quarters. It was capacious compared to that of the Segundo and doubled as a dining room or off-duty lounge for the flagship’s officers. The wardroom featured a pair of wooden tables in its center with bench-style seating and sleeping berths along both sides.54 The berths were double-stacked, sat upon a chest of wooden drawers, and had privacy curtains like a sleeper on a Pullman car. The wardroom also had a fan and was trimmed in wood, most of it varnished—something you’d never find aboard an American sub.55 Part of the officers’ quarters sat next to a bomb magazine though, so not every aspect was luxurious.

  Dolls softened the surroundings of many Sixth Fleet subs. The I-401 had one in her wardroom.56 A demure, white-faced Japanese woman dressed in an exquisite kimono, she was a sentimental item intended to remind the officers of home. Though no Betty Grable pinup, many officers found comfort in her.

  Ariizumi’s and Nambu’s cabins were located next to one another near the control room. Both cabins were small with a tiny desk, bed, and hardly enough room to change one’s mind. Nevertheless, they provided the privacy necessary for command.

  NO. 4 COMPARTMENT (STARBOARD): CREW’S BERTHING No. 4 was the last crew compartment in the forward half of the boat. Enlisted men were segregated from their officers aboard Sixth Fleet subs, just as they were in the U.S. Navy. But sealing 200 men inside a cramped combat sub bred an informality that softened differences in rank. Even the dress code was relaxed. An enlisted man’s uniform consisted of a short-sleeved shirt, shorts, socks, rubber-soled shoes, and a short-brimmed cap.57 Just as there was leeway in what U.S. enlisted men wore aboard a fleet boat, the I-401’s men exercised similar sartorial discretion. Some went shirtless, limiting themselves to shorts and straw sandals; others wore only a fundoshi, or loincloth, when working in the hotter parts of the sub. Officers were more regular in their dress, but the longer the patrol, the quicker they dispensed with formality.

  Nothing affected submarine fashion like high temperatures. Some days it was so hot, men slept naked.58 The I-401 had air conditioning, but South Seas heat easily overwhelmed her cooling plant. Humidity was also a problem. A Seiran’s avionics were particularly vulnerable, as was the sub’s electronic equipment. The airplane hangar was packed with desiccant to reduce humidity,59 but for the men inside the sub, it was a dripping steam bath.

  Not much attention was paid to the habitability of Sixth Fleet subs.60 Creature comforts were few, and crews didn’t receive the rest they needed after each mission. Add to this a shortage of trained men, and efficiency declined as the war progressed.

  The crew offset their grim industrial setting with a few personal touches. Some of the most popular were Japanese keepsake dolls. Mothers, sisters, and girlfriends made imon ningyo for their sons, brothers, and boyfriends to keep them company on their long, lonely voyages. They were a familiar sight in the crew quarters, and it wasn’t unusual to hear a man bid his companion good night before turning in.61 At least he knew he wouldn’t die alone.

  Sub hygiene was also questionable. Though there was water for brushing teeth,62 many men chewed gum instead.63 Most grew beards,64 but haircuts were given to those who wanted them,65 especially since a shaved head helped prevent lice (a constant problem in close confines). Submarine living conditions were undeniably tight. Still, Japanese home life had prepared crews for close quarters and they quickly adapted.

  One of a crew’s few personal luxuries was smoking. Favorite brands included Kinishi, Homare, and Cherry,66 and most men were heavy smokers. Smoking was allowed in many parts of the sub, but cigarettes were in such short supply they were considered a treat.

  Another problem affecting the Sen-toku subs was rats: it was impossible to keep them off the boats. This wasn’t unusual.67 U.S. subs were plagued by cockroaches. One Sixth Fleet sub set up a rice feeder for their rats; others adopted them as pets.68 Inevitably, there was the odd sailor who trained them for his personal enjoyment. But having rats wasn’t all bad. Sixth Fleet crews often joked, “Safely returning subs have rats. Sinking ones don’t.”69 They had a point.

  NO. 5 COMPARTMENT (PORT): CONTROL ROOM Though relations on a sub could be informal, that didn’t extend to the control room, where only the strictest protocol prevailed. The control room was the sub’s nerve center. It was where diving, surfacing, and navigation functions were managed as well as where every important environmental system was monitored. Though the conning tower duplicated many of these stations, they were generally limited to combat use.

  The I-401’s control room was far larger than that of a Balao-class sub. (There was even a head for the convenience of those on duty.) Controls included the hydraulic vent manifold, which flooded a sub’s ballast tanks, enabling it to submerge; the high-pressure blow manifolds, which emptied the ballast tanks of water so the sub could surface; the trim manifolds, which pumped water from one ballast tank to another (or into the sea) to help a submerged sub achieve equilibrium; the air and ventilation systems, which kept the crew breathing; and the main distribution panel, which managed the sub’s electrical supply. The sub’s radio shack, radar room, ship’s office, engineer’s log room, and access to one of its main ammunition scuttles were also located in the compartment. In fact, the only vital systems not found in the control room were the physical propulsion systems, torpedoes, defensive armament, and food prep. Nevertheless, the control room kept close tabs on all of them.

  Although a sub’s operating principles were basic in nature, her engineering was not. Every inch of space in the control room was covered by a bewildering array of dials, levers, valve wheels, gauges, meters, circuit breakers, and control knobs. Nothing made sense unless you’d been to sub school. The piping schematic alone would have confounded anyone unfamiliar with sub design. Crew members might have preferred sinking enemy ships, but the truth of sub life was more prosaic; much of their time was spent protecting against the sea’s invasiveness.

  BALLAST TANKS Just as controlling altitude is vital to a plane’s operation, maintaining buoyancy is critical to a sub’s survival. Unsurprisingly, the I-401 had four types of ballast tanks. The first were the main ballast tanks, which wrapped around the underside of her pressure hull. When a sub wanted to submerge, she filled these tanks with seawater, which entered through flood ports located near her keel. Once flooded, the tanks grew heavy, pulling her downward. When the sub needed to surface, compressed air was used to blow seawater out through the main vents, increasing her buoyancy.

  The main ballast tanks did the heavy lifting of surfacing the boat, but other ballast tanks were necessary for specific maneuvers. For example, when a sub needed to dive in a hurry, the negative tank was flooded. Located underneath the forward part of the sub, it quickly gave the boat the descent angle she needed to dive. The negative tank was especially helpful when the sub was on the surface and had to escape a fast-approaching enemy. In turn, when a sub needed to surface in a hurry, the safety tank was emptied, or “blown.” Located amidships to help maintain the sub’s balance, “blowing the safety” was the fastest way to restore buoyancy in an emergency.

  Variable ballast tanks were considered “variable” because they could be used to store either fuel or seawater. This was necessary because when a sub consumed fuel, it lost weight and became more buoyant. To compensate, seawater was pumped into the variable tanks to make up the difference.

  Surfacing, submerging, and maintaining equilibrium were three critical tasks that took up much of the control room’s focus. Given their importance, one of the most common expressions aboard a Japanese submarine was “Blow the main tank!” Blowing means using compressed air to force water out of the tank, thereby improving buoyancy and allowing the sub to surface. On a somewhat amusing note, Nambu used a Japan-ized version of the order: “Men tanku burou!” which was phonetically equivalent to the English.

  HELM AND DIVE PLANES A sub constantly had to switch between the two-dimensional world on the surface and the three-dim
ensional one below. To help with this, the control room had three “steering” stations. The first was the helm, a large metal wheel used to control the rudder in the stern. The helm directed the forward motion of a sub both when surfaced and submerged. The helm wasn’t enough for steering underwater, however—a sub required dive planes as well.

  The dive planes were two sets of fins located on the outside of the I-401’s hull, one set near the bow, the other near her stern. The dive planes enabled her to ascend or descend depending on their angle. When operating on the surface, the I-401 kept her dive planes rigged in an upward position. She only lowered them to navigate underwater. At first glance, the I-401’s bow planes hardly seemed large enough to control the sub,70 but Nambu found them more than adequate.71

  Two dive planesmen stood side by side at separate steering stations, one controlling the bow, the other the stern. An array of gauges stared them in the face, including a depth gauge, a speed indicator, and a bubble indicator, which showed the boat’s up-or-down angle. An experienced planesman could keep the boat so steady, the sub’s depth gauge never budged an inch.

  NAVIGATION Since the central helm station and master compass were located in the control room, much of the sub’s navigation was done there. It had a small table for manually plotting the sub’s position and tracking enemy targets. Secondary firing solutions were also developed there, to reconfirm those made in the conning tower.

  Sub navigation was not very sophisticated during the war. If a sub knew her position within 50 miles of her actual location, it was considered accurate. Celestial navigation was common, and many a navigator scrambled onto a sub’s bridge at night to read the stars. Plotting a sub’s position was as much art as science.

  RADAR The I-401 carried three different types of radar, all of which had a station in the control room and outlets on the aft part of the sail. The Mark 3 Model 1 air search radar was used to spot planes, while the Mark 2 Model 2 was used to find surface ships. It also had a nondirectional antenna for passive radar detection as well as an omnidirectional antenna, a direction finder, and a target-detection antenna.72

  The principle behind radar was almost magical. The I-401 would send out a radio wave that “bounced” off an object, like a ship or plane, and returned to the sub, providing the target’s range (distance) and bearing (direction). If the I-401 tracked the target long enough, it was also possible to deduce its course and speed. The distinctive circular scope and secondhand sweep of light were intended to ensure that the enemy never approached the sub without warning. That was the theory at least. But Japanese radar was still in its infancy and prone to break down. It might have been an improvement over binoculars, especially in poor weather, but it was frequently frustrating.

  RADIO ROOM The radio room, where the I-401 connected to the outside world, was located on the port side of the control room. It would soon become a favorite place for Seiran pilots to loiter while the sub was under way.73 The communications officer responded to a plethora of messages via shortwave radio—much to Nambu’s annoyance, since he preferred radio silence. Orders from Japan were transmitted at night, when a sub was surfaced, but the I-401 could also receive messages at periscope depth via a special antenna mounted on her bridge.

  NO. 5 (STARBOARD): AUXILIARY ROOM Opposite the control room on the starboard side of the sub was a special compartment, which at least one source claims was used to overhaul Seiran engines. A hatch 31 inches in diameter connected the compartment to the control room.74 There was also an overhead access tube leading to the aircraft hangar.§ 75 Seiran engine maintenance was usually conducted in the hangar, which is not surprising, since it is hard to imagine how they fit an Atsuta engine into the auxiliary room even on a sub as large as the I-401.

  Two of the sub’s supplementary generators were located in the auxiliary room, as was the sub’s turbo blow, which was used to empty the main ballast tank when the sub was surfaced and (God forbid given how high she sat in the water) required more freeboard.

  GALLEY Every sub has a galley. The I-401’s was located adjacent to the auxiliary generators.76 One can imagine the difficulty in preparing three meals a day for 200 men. Somehow, the I-400 cooks managed. Three freezer lockers below the galley deck kept food cold,77 and four78 oversize steam kettles turned out large quantities of rice to provide the crew with the much-cherished staple.79

  Food was the best part of life aboard the Sen-toku subs. It was far better than anything the Imperial Japanese Army received, and there was plenty of it. Rice was served at every meal, and the galley even managed delicacies like cow tongue, boiled eel, and sweet bean paste. Staples included broiled fish, shrimp or vegetable tempura, beefsteak, pork cutlets, eggs, pickled horseradish, dried seaweed called nori, chestnuts, fresh oranges, canned peaches, pears, and pineapples, fruit juice or sodas, and miso soup for breakfast.80 Green tea was consumed in vast quantities, and coffee less so, though it was available. Evening snacks included noodles, or biscuits with milk.81 Some Sixth Fleet subs even had ice cream, though it was usually reserved for special occasions like the last meal before a dangerous mission.82 In fact, after a few weeks at sea, one of the I-400 cooks yearned for simpler fare, such as brown rice and pickled plum.83

  An onboard nutritionist planned every meal84 even though fresh vegetables ran out by the tenth day at sea. After that it was canned food morning, noon, and night,85 with onions thrown in for variety. Tinned vegetables were especially unpopular, since they tasted like sand and ashes.86 There were only so many canned sweet potatoes a crew could eat before complaining set in. Bottled vitamins were available at each meal, since it wasn’t unusual on longer voyages for mild cases of beriberi to develop.87 The real problem with the I-401’s food supply though was that the sub’s size greatly reduced the number of flying fish that jumped on her deck. This limited a much-appreciated supplement to the standard fare—yet another consequence of being big.

  CONNING TOWER Immediately above the control room was the I-401’s conning tower, which was used for combat operations. It was a dark, cramped space 8 feet in diameter and 20 feet long,88 only 2 feet longer than the Segundo’s conning tower. When nine men squeezed in during battle stations, the compartment became impossibly tight. Nambu could make a ship or aircraft sighting through one of two periscopes, calculate firing solutions, and launch torpedoes from the conning tower. There were also duplicative sound, radar, and helm stations, a further example of how redundancy was a central design feature in submarines.

  One of the worst things a sub could face was its conning tower being flooded, either by accident or by an enemy blowing a hole in its plating. The situation was especially dangerous aboard the I-401, because the sail’s offset position could easily heel the sub onto her side.89 The sail had extra steel plating to protect against such an event,90 but it was still a risk.

  NO. 6 COMPARTMENT: PORT AND STARBOARD ENGINE ROOMS The I-401’s engines were located in two compartments aft of the control and auxiliary rooms. Unlike the Segundo, where the engine rooms were sequential (one forward, one aft), the I-401’s engine rooms flanked each other with a hatch connecting the port and starboard compartments. The sub’s four diesel engines were the only ones of their kind in the Sixth Fleet,91 but their defining characteristic, besides their unusual size, was how temperamental they could be. Each engine was rated at 2,250 shp and was connected to one of two propeller shafts via reduction gears in the aft section of the compartment.92 With a clean bottom, the I-401 could generate a top speed of 20 knots surfaced and up to 7 knots submerged (though not for long).93 She might have been big, but she was by no means slow.

  Up to four engines could be used on the surface to power the I-401, though one engine was usually delegated to charging her batteries. However, her diesels couldn’t operate below periscope depth, so batteries were used to drive an electric propulsion system.

  Nambu’s sub carried approximately 500,000 gallons of diesel oil, enough to fill 15 railway tank cars.94 Fuel was in such short supply that
the Imperial Japanese Navy cut it with soybean95 and pine oil.96 This means it burned dirty and left a black exhaust cloud for enemies to follow. Unfortunately, nothing could be done about it.

  The engine compartment also housed several vapor-compression stills. Each still (called an evaporator) turned the ocean into fresh water by boiling it. Their output was never as advertised, so there was little water for personal use and none for showers.97 This partly accounted for the sub’s unmistakable smell of grease, diesel fumes, hydraulic fluid, male sweat, cigarette smoke, and whatever was being cooked for lunch. After a while, nobody cared.

  NO 7. COMPARTMENT: PORT AND STARBOARD MANEUVERING ROOMS Just aft of the main engine rooms were the sub’s port and starboard maneuvering rooms. If Nambu wanted to increase speed, the information was relayed via engine annunciators from either the conning tower or the control room to an electrician’s mate in the maneuvering cubicle. There he manipulated a set of long metal levers to power the sub’s electric motors either up or down, depending upon Nambu’s order.

  The I-401 had two 1,200 shp electric motor-generators, one for each propeller shaft. The electric motors drew electricity from storage batteries used to drive the sub when submerged. If the engine room was defined by noise, the motor room was defined by heat. In fact, the electric motors generated so much heat, the men worked shirtless. The sub’s humidity also shorted out the compartment’s electrical distribution panels, making for constant problems.98