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IJN I-58

Diesel-Electric Attack Submarine

Imperial Japan | 1944

"The IJN I-58 was the last B-3 series type submarine to be produced though twenty-one such vessels were planned."

Authored By: JR Potts, AUS 173d AB | Last Edited: 05/30/2017 | Content ©www.MilitaryFactory.com | The following text is exclusive to this site; No A.I. was used in the generation of this content.
The last Japanese submarine built in the B-3 type series family became the I-58. She was laid down on December 26th, 1942, launched on June 30th, 1943, and completed on September 7th, 1944, at the naval yard in Yokosuka, Japan - the home port of the mighty Battleship Yamato. She was launched in early December 1944 and was assigned to the IJN 15th Submarine Section with Lt. Commander Mochitsura Hashimoto in command beginning in June of that year. The I-58 is best known for the sinking of the USS Indianapolis and served as a mother-ship to several Kaiten "suicide" manned torpedoes. She survived through to the end of World War 2 before being purposefully scuttled in 1946.

The B-Type Series

The previous B-1 and B-2 series boats had a range of 14,000 nautical miles. As such, the B-3 type series was designed as a long-range patrol boat able to operate deep within the vast Pacific Ocean - the largest ocean body on the planet. She carried 842.8 tons of fuel oil allowing her to range out to 21,000 nautical miles at 16 knots. The maximum diving depth of 100 meters (330 feet) remained the same throughout all the B-series boats including the B-3. The increased range, however, was a remarkable achievement in World War 2 submarines. This allowed the B-3 to patrol, target and sink any and all allied shipping within her increased operating range. The Imperial Japanese Navy (IJN) wanted more such submarines but with all of her military services competing for Japan's limited available resources to fight the war, the IJN decided to build fewer but larger boats with extended range.

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Between September and December of 1944, I-58 had her 140mm deck gun removed to make the needed room for the Kaiten suicide torpedo compartments. Two compartments were initially fitted and these were joined by a Type 22 surface/air-search radar system fitted to the top of the aircraft hangar (the I-58 housed a Yokosuka floatplane). An E27/Type 3 radar system was fitted to the bridge. I-58 reported to the IJN Sixth Fleet's SubRon 11 Group for training in the Inland Sea.

Suicide Torpedoes

On December 2nd, 1944, a special conference was held at IJN Sixth Fleet to evaluate the battle results of the first Kaiten "manned torpedo" mission at Ulithi. In attendance were 200 staff officers and various other personnel and the meeting took place onboard the Sixth Fleet flagship IJN Tsukushi Maru. After review of the available reconnaissance photos and absorbing the after-action reports from the participating Japanese commanders, it was decided that the American Navy had lost three aircraft carriers and two battleships in the foray. In reality, however, no American carriers or battleships were ever sunk. These type of inaccurate or exaggerated claims covering enemy losses was common to both sides during the war, proving great for moral but horribly bad for war planning decisions.

Based on these reported successes, the Kaiten was viewed as a viable offensive weapon. These "kamikaze" torpedoes required a crew of two men and were 45 feet long with a 3,000 pound warhead.

On December 4th, 1944, the I-58 was reassigned to SubDiv 15 as part of Vice Admiral Miwa Shigeyoshi's Sixth Fleet. Four days later, the vessel was assigned to Kongo (Diamond) Group along with submarines I-36, I-47, I-48, I-53 and I-56. This group was charged with attacking the American Fleet across five anchorages with their Kaiten torpedoes. Specifically, the I-58 is given the assignment of targets at Apra Harbor in Guam, the attack to commence on January 11th, 1945.

The I-58 was transferred to Otsujima to undergo Kaiten launching training during the period from December 19th, 1944 to December 24th, 1944. She then departed from Sasebo towards Kure for resupply and rearmament. On December 29th, she headed out of Kure towards Otsujima. Two days later, the I-58 receives four Kaiten torpedoes and their applicable crew and then heads out to Kure with submarine I-36. The group arrived near Guam on January 6th, 1945. Soon enough, I-58 received word from a scout plane (Nakajima JC6N2 Saiun-Kai "Myrt") that several enemy vessels were at Apra harbor - an escort carrier, two destroyers, one submarine, 20 transports and four floating docks. The decision was to penetrate the harbor and launch the Kaiten torpedoes on January 11th, 1945.

Flawed Reporting Leads to Flawed Decisions

I-58 launched all four of her Kaitens and, as Lt. Commander Mochitsura Hashimoto left the area, he took note of two columns of smoke rising. His quick retreat was forced upon him as Kaiten Number 4 self-detonated immediately after its launching. On January 22nd, 1945, I-58 arrived at the Japanese base at Kure and Hashimoto learned that he had been credited with sinking an American aircraft carrier and a large merchant ship (an oiler). Unbeknownst to Hashimoto, this grand claimed sinking of the two ships would also prove to be an incorrect assessment of the action but it served to bolster the use of Kaitens in future assaults.

Operation TAN 2

I-58 returned to Japan to rearm with four new Kaiten suicide torpedoes and their respective crews. I-58 was then ordered to attack the American Fifth Fleet of 450 ships stationed near Iwo Jima as part of Operation Detachment. The Americans had captured the island and its all-important Motoyama airfields. I-58 and I-36 are grouped once again as part of the Shimbu attack group charged with targeting island communications at Iwo. I-58 leaves Hikari on February 28th, 1945, now fitted with a Type 13 air-search radar system.

On March 1st, 1945, I-58 left the port at Kure, fully armed and loaded and voyages through the Bungo Straight. Several close calls with American spotted planes forced the submarine under but limited her detection. On March 7th, I-58 surfaced as standard practice to recharge her depleted batteries (needed for submerged operations). Her original mission was to attack the anchored shipping vessels off of Iwo but this command was later repealed as the Combined IJN Fleet is called to cease operations around Iwo Jima and proceed to Okino Torishima (Douglas Reef) to participate in a new Operation named "TAN No. 2". Hashimoto decided to jettison two of the four Kaitens and proceeded at flank speed to Okino Torishima.

TAN 2 was a joint Japanese Army and Navy attack plan involving twenty four, twin engine Yokosuka bombers each carrying one 1,763 pound bomb on a kamikaze mission from Kanoya airfield to attack USN ships at Ulithi harbor. I-58's station was to be a radio beacon for the bombers to follow to Ulithi. Six bombers made it and hit the carrier USS Randolph CV-15 resulting in moderate damage to her structure. I-58 found no viable targets herself to fire on and returned to Hikari, debarking her two remaining Kaiten's and their crews. The I-58 then relocated to Kure and underwent more Kaiten training in the inland sea sometime in late March of 1945.

War Along the Back Doorstep

The Tatara Group, with I-58 in her ranks, was created to attack the American Fifth Fleet anchored off of Okinawa. The fleet consisted of 40 carriers, 18 battleships, 20 cursors, 200 destroyers and more than 1,000 support ships of all kinds for participation in Operation Iceberg - the invasion of Okinawa. I-58 had arrived at her station from Hikari on April 4th, 1945, with Kaitens in the hold and found the air was filled with American aircraft, forcing her to stay submerged during daylight hours and force use of her snorkel to replace the stagnate internal air. Foul weather soon plays into future I-58 actions in the region and the constant diving has depleted her batteries.

Rush to Okinawa

A special attack surface force - including the Battleship Yamato, seemingly on course for its own suicide mission - was steaming towards Okinawa to attack alongside the waiting IJN submarines. I-58 was to penetrate the American invasion fleet along Okinawa's west coast and deliver its potent Kaiten payload. This would serve to support the subsequent attack of the Yamato and relieve the beleaguered Japanese forces on the island. However, on April 7th, Hashimoto received word that the Yamato was sunk by the Allies. For the next eight days, the I-58 repeatedly tried to break through the Fifth Fleet's Anti-Submarine Warfare (ASW) defenses but failed and was eventually ordered back towards Guam.

On April 25th, 1945, surfaced to recharge her batteries and spotted a Allied hospital ship on radar. Hashimoto let the surface ship pass by unmolested but is herself spotted by no less than three American destroyers who immediately give chase. While being depth-charged, the I-58 dove to depths as low as 300 feet and ultimately avoided destruction. She arrived at Hikari and unloaded her Kaitens and crew.

The I-58 arrived at Kure in May 1945. Some modifications were made to her structure to allow for the fitting of an additional pair of Kaiten manned torpedoes. As such, the hangar and catapult used to manage the internally-housed scout floatplane were removed. I-58 now carried six Kaiten suicide torpedoes, each with their own access tube. With her extended range and Type 22 surface / air radar (relocated to the conning tower) in addition to her new Type 3 sonar, making for over-the-horizon air recon by patrol aircraft no longer required. Kure was then targeted by American bombers but the I-58 remained unscathed - other submarines were not as fortunate. Lieutenant Commander Hashimoto continued to train his crew and patrol against allied shipping in the area.

The USS Indianapolis

On July 26th, 1945, the heavy cruiser USS Indianapolis (CA-35) arrived at speed in Tinian in the Marianas, secretly delivering parts - unescorted - of the nuclear material (Uranium) for the atomic bomb "Little Boy" to be (eventually) dropped on the Japanese city of Hiroshima. I-58 happened to be patrolling the area between the Marianas and the Philippines and was in the Philippine Sea near Leyte at the time. The USS Indianapolis left Guam and headed for Leyte (without an escort as her mission was deemed of top secret importance) and she was not fitted with any type of ASW equipment. To promote some level of self-defense measures against enemy submarines, surface crews took to "zig-zagging" routes while at sea. The USS Indianapolis followed her training but poor visibility soon hampered her journey.

At 2305 hours, IJN I-58 surfaced and moved south when Lieutenant Commander Hashimoto spotted a surface vessel approaching from the east, roughly out some 11,000 yards. The ship was further identified as a United States Navy Idaho-class battleship, outlined by the rising moon, and making 12 knots along a straight course. The decision was made to attack the enemy vessel using conventional torpedoes at 1,650 yards. While advantage was still his, Hashimoto ordered the firing of six Type 95 torpedoes towards the American ship. He observed three spaced torpedo hits along the starboard side of the battleship. The first occurred near the bow and the second was registered at turret number one. The third torpedo struck the vessel square-center, just under the bridge, near turret number 2. Hashimoto decided another attack was necessary to bring the American ship down and ordered the I-58 to dive. This helped to keep his submarine from detection. Two of her forward torpedo tubes were ordered reloaded. By the time I-58 came to periscope depth the Indianapolis had already sunk - in just twelve minutes. Hashimoto took his boat and crew out of harm's way due North at full speed. He signaled to the IJN Sixth Fleet that the I-58 had confirmed the sinking of an American battleship.

The USS Indianapolis crew was in the water for five terrible days, under threat of dehydration, exposure to the Pacific sun and salty waters and the danger of shark attacks. Many died due to the non-response and bumbling on the part of the USN - a distress signal had been sent from the USS Indianapolis but three party recipients failed to act. Even an intercept of the I-58s claim that they had sunk a battleship is not investigated. The Indianapolis' lack of an escort vessel also doomed much of her crew. In normal USN operations, a destroyer (ASW equipped) was assigned to a capital ship like the USS Indianapolis. If such an assignment had been made to the Indianapolis, the destroyer may have foiled the I-58's attack. The decision proved a highly fatal one on many fronts. To put the vessels sinking into perspective, the USS Indianapolis CA-35 was crewed by a total of 1,196. 300 perished with the sinking vessel, and 883 were lost in whole to the event. Half died of drowning and others to shark attacks. In the end, only 316 sailors were left alive and these were only found by chance by a PV-1 Ventura on routine patrol. A full rescue operation soon ensued. For all their suffering, the crew of the Indianapolis went through hell just one month shy of the end of the war, making her one of the last USN ships to be lost to enemy action. To her name, she carried 10 Battle Stars for actions in World War 2.

Life for the I-58 Crew Steams On

The crew of I-58 was proud to have completed their duty that resulted in the destruction of an enemy ship. They continued on-mission after refueling and receiving more torpedoes. On August 9th, 1945, while on patrol off Aparri, she spotted a convoy that included the escort carrier USS Salamaua (CVE 96) along with three destroyers and ten "Liberty" ships joined by on their way to Okinawa. Hashimoto decided to attack with Kaiten 3, 5 and 6. Problems began to emerge when number 3 and 6 developed engine malfunctions. Number 5 was cleared to launch and Number 4 joined her shortly. A destroyer, the USS Johnnie Hutchins (DE-360), saw what appeared to be a whale approaching. That incorrect observation was soon rectified to reveal the incoming object as none other than Kaiten Number 5. The American crews opened fire and sunk the suicidal crew, their submarine becoming their coffin at sea. Kaiten Number 4 was depth-charged and presumed sunk. A third submarine was reportedly seen and, when depth-charged, secondary explosions caused a 30 foot geyser - indicating a direct hit. DE-360 and her crew were credited with the sinking of two enemy vessels and a possible third.

Southeast of Okinawa, on August 12th, 1945, the I-58 sighted an enemy destroyer and a seaplane tender and launched the remaining Kaiten Number 3. The small vessel approached within 2000 yards but was run over by the destroyer, forcing her to surface and consequently self-detonate, killing her Japanese crew. This proved the Kaitens were not the IJN weapon of choice for they risked much for mostly little return - they were a danger to their host submarines, difficult to maneuver and offered poor visibility in identification of their targets. Furthermore, they cost much needed war-making material and explosive content along with two trained Japanese sailors on their suicidal missions.

Her Fighting Days Are Over

Arriving at the Kure base on August 18th, 1945, Hashimoto learned of the ultimate Japense surrender two days before and though it to be an American propaganda trick. However, sanity prevailed within time and he delivered the news to his crew and officially surrendered the boat to the Allied representatives on September 5th, 1945. Hashimoto and the crew went home to a devastated homeland and their honor irrevocably damaged.

One-Hit Wonder

In post war reviews, it became apparent that the only ship sunk by I-58 was in fact the USS Indianapolis, and that was by conventional torpedoes no less - despite her reliance on the Kaiten suicide torpedoes. I-58 was towed to 300 feet of water off Goto Island, Japan on April 1st, 1946 and scuttled - her legacy intact but over nonetheless.

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Power & Performance
Those special qualities that separate one sea-going vessel design from another. Performance specifications presented assume optimal operating conditions for IJN I-58.
2 x Kampton Mk 22 Model 10 diesel engines generating 4,700bhp; submerged electric motors producing 1,200 horsepower; 2 x shafts.
17.7 kts
20.4 mph
Surface Speed
6.5 kts
7.5 mph
Submerged Speed
21,000 nm
24,166 miles | 38,891 km
The bow-to-stern, port-to-starboard physical qualities of IJN I-58.
356.5 ft
108.66 meters
O/A Length
3.5 ft
1.07 meters
17.0 ft
5.18 meters
Displacement (Submerged)
Available supported armament and special-mission equipment featured in the design of IJN I-58.
6 x 533mm (21-inch) torpedo tubes (all bow-facing); 19 x Type 95 torpedoes.
6 x Kaiten manned torpedoes (later)
1 x 140mm (5.5-inch) L/40 11th Year Type Naval deck gun.
2 x 25mm Type 96 anti-aircraft guns
Air Arm
Available supported fixed-wing / rotary-wing aircraft featured in the design of IJN I-58.
1 x Yokosuka E14Y2 "Glen" floatplane
Ships-in-Class (3)
Notable series variants as part of the IJN I-58 family line as relating to the Type-B Mod. 2 group.
I-54; I-56; I-58
Global operator(s) of the IJN I-58. Nations are displayed by flag, each linked to their respective national naval warfare listing.
National flag of modern Japan

[ Imperial Japan ]
1 / 4
Image of the IJN I-58
The I-58 submarine prior to its scuttling on 1946
2 / 4
Image of the IJN I-58
Close-up detail view of the sail of the I-58 submarine
3 / 4
Image of the IJN I-58
The I-58 submarine alongside the I-53
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Image of the IJN I-58
A view inside the torpedo room aboard the I-58 submarine

Mission Roles
Some designs are single-minded in their approach while others offer a more versatile solution to seaborne requirements.
Some designs stand the test of time while others are doomed to never advance beyond the drawing board; let history be their judge.
Going Further...
IJN I-58 Diesel-Electric Attack Submarine appears in the following collections:
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