The Wreck of the IJN Mogami
September 14, 2019
On May 8th, 2019 the R/V
Petrel located the wreck of the Japanese heavy cruiser
Mogami in 4,760 feet (1,450 meters) of water in the vicinity of the Surigao Strait.
Painting of Mogami, 1944
Mogami was the lead ship of her class of heavy (Class A) (originally light [Class B]) cruisers, laid down on October 27th, 1931. Under the terms of the London Naval Treaty, cruisers were limited to a maximum gun bore of 8'' and maximum normal displacement of 10,000 tons, but the total tonnage of heavy and light cruisers was also limited. With the
Takao class under construction, the IJN was out of offical tonnage for heavy cruisers.
To get around this in the future, the IJN's design team, lead by Adm. Kikuo Fujimoto designed the class with provisions to have the 155mm triple mounts replaced with 203mm twin mounts.
As-built,
Mogami displaced 8,500 tons standard, 13,760 tons full, and was armed with five triple 155 mm /60 caliber guns, two twin 127/40 89-shiki guns, two single 40mm /62 caliber HI 91-shiki AA guns, and four triple 610mm torpedo tubes with a set of reloads for each, giving a total of 24 torpedoes. She had an impressive top speed of 37 knots.
Mogami, as built, in 1935
A drawing of Mogami and Mikuma in 1935, the main difference between them was the style of the mainmast.
In an effort to save on weight,
Mogami and
Mikuma were constructed with electrically welded hulls and significant use of aluminum in the superstructure. These ships were plagued with issues, and underwent a significant rebuild shortly after they were launched due to the investigation prompted by the
Tomozuru Incident.
The brand-new torpedo boat
Tomozuru capsized in March 1934, with the loss of 100 crewmembers. During the investigation, it was determined that many Japanese warships were vastly overloaded and top-heavy, including the brand-new
Mogami class. This incident caused major damage to Fujimoto's reputation, but he was recalled to his office with the recognition that he was given design requirements that cut ship safety and integrity far too much. However, he died the very next day, and the later events would result in many of his prodigies being dismissed as well. This would have significant consequences for the designs of later warships.
Compounding the issue of instability, the welded hulls were weak, with welds splitting when the main battery was fired, and during the 4th Fleet Incident of 1935, they developed major cracks in their hulls in a typhoon. The IJN did try and remedy these major shortcomings, with a major reconstruction of
Mogami and
Mikuma starting in 1936 and running to 1938.
1,120 tons were added to
Mogami, 1,063 tons of which were taken up with hull reinforcement and additional bulges to improve stability. This increased the beam from 19m to 20.2m and resulted in the speed dropping to 35 knots. Other changes at this time were the removal of the 40mm guns, several stowed torpedoes which dropped the total to 18 weapons, and the addition of two more twin 127mm mounts, four twin 25mm mounts, and two 13mm MGs.
There were few changes until 1939, when Fujimoto's plan was put into effect. The triple 155mm guns were all removed, and twin 20 cm/50 3rd Year Type No. 2 mounts (Actual bore of 203.2mm) were put in their place. But despite the plans to do so, there were many issues. The 155mm turrets needed a larger diameter roller path, so when it was time to replace them, the 203mm guns were fitted to bigger turrets to actually fit the rollers properly. Another issue was that the 203mm guns were longer, which prevented the guns of Turret Two from being lowered past 12 degrees when pointed directly ahead.
During these operations, the catapults were replaced with more modern ones, and the number of torpedoes was restored to the full 24 as originally built.
Drawing of Mogami and Mikuma after their 1939-1940 rebuilds, also showing the differences between the two ships.
In late 1941 into early 1942
Mogami operated with Cruiser Division Seven in the southwest Pacific, participating in the invasions of Malaya, Kuching (British Borneo), Sumatra, and Java. On February 28th, 1942 she was involved in the Battle of Sunda Strait, firing six Type 93 torpedoes at USS
Houston and HMAS
Perth. While the allied cruisers were sunk, the Japanese paid for their wild torpedo fire, with
Mogami probably being responsible for the sinking of a Japanese minesweeper and transport, and serious damage to three other ships, including a hospital ship and the command ship of the IJA force that was landing that night.
The next major action for
Mogami would not end nearly as well for the cruiser, since in June 1942 CruDiv7 was attached to the Operation MI force heading to Midway Atoll. At 2138 on June 4th, lookouts on the flagship of CruDiv7 (
Kumano) spotted the surfaced US submarine USS
Tambor (SS-198). The order is given for the line of cruisers to make a turn to port to evade any torpedoes that might have been launched.
Over the next few minutes, the four cruisers make turns of various tightness, with
Suzuya nearly hitting
Kumano. But five minutes after the order was given, the last two ships in the line,
Mogami and
Mikuma collided. The last moment maneuvers by
Mogami helped mitigate the 28-knot impact between the 13,000 ton ships, but the damage was still severe.
Mogami's bow crumpled down to Turret One, forty feet of steel was crushed back and almost 90 degrees to port, and she was dead in the water.
Mikuma suffered most of her damage above the waterline, near the bridge tower, though it was still a 20x6 meter gash with bent-in plating, along with a leaking tank of fuel oil.
Both
Mogami and
Mikuma were detached from CruDiv7 and sent them to the west at
Mogami's best speed of 12 knots. Lt. Cdr. Saruwatari Masayushi, Mogami's damage control officer, did a fantastic job at improving his ship's chances. He led teams to shore up the bow watertight compartments and ordered the disposal of as much flammable material as possible, including all 24 of the Type 93 torpedoes.
At 0630 the next day an American PBY flying boat spotted the damaged cruisers, and they were subjected to several air attacks from Midway by Marine Dauntless and Vindicator bombers, and later by Army B-17s, with only light damage and few casualties.
June 6th, 1942 saw the American carriers turn their planes towards the battered CruDiv, now joined by a pair of destroyers. The first attack by dive bombers was at 0950 from USS Hornet (VB-8 and VS-8 with extras) scored near misses on
Mikuma, but landed two hits on
Mogami. One hit Turret Five directly, killing every man inside, the second passed through the aircraft deck and ended its travel by detonating in the torpedo room. Had she still been carrying her Type 93s, this could very well have been a fatal hit. Despite the fires and the loss of all three floatplanes, the fires were put out in about an hour.
Painting of Mikuma's AA gunners firing at the American dive bombers. Three bombers were shot down by the Japanese fire, none of their crews survived.
Next came
Enterprise's dive bombers, at 1245 and though the cruisers were now making 20 knots,
Mogami took two more bomb hits, one to the aircraft deck and one ahead of the bridge, though these hits only caused moderate damage.
Mikuma was not so lucky, and suffered several devastating hits that would ultimately doom her.
The last hit to
Mogami stuck the aircraft deck again, the 1000 pound bomb killing nearly every man in the sickbay and starting a large fire. Saruwatari made another hard call and sealed off several hatches in the area to contain the fire, even though there were still men trapped inside.
Despite the loss of
Mikuma and most of her crew, and 90 killed and 101 wounded on
Mogami, the ship survived to fight another day.
Starting in September 1942,
Mogami underwent her last major modification, with the addition of a large aircraft deck on the stern. Except for small details, this would be her final configuration.
The rebuild more than tripled
Mogami's aircraft capacity from three to eleven, with the removal of Turrets Four and Five, the conversion of the magazines for those turrets into magazines and fuel tanks for the aircraft, and adding a sprawling arrangement of tracks to store and transport the aircraft.
Originally the aircraft were supposed to be the brand new Aichi E16A1 Zuiun (Allied reporting name 'Paul'), but since there weren't enough of these planes to go around, Mogami got three Mitsubishi F1M2 Type 0 and four Aichi E13A1 Type 0 planes at first ('Pete' and 'Jake' respectively).
Other changes involved the addition of ten triple 25mm AA guns, the removal of the twin 25mm guns, as well as the 13mm guns. She was also fitted with a 1-shiki 2-go/Type 21 air and surface search radar.
Mogami would see some action over the rest of 1943 into 1944, such as the explosion and sinking of
Mutsu, some of the Allied raids on Rabaul, the Battle of the Philippine Sea, and received another refit in June 1944 that added several single 25mm guns around the perimeter of the aircraft deck (single mounts denoted by 'X' on the drawing above.
On October 22nd, 1944
Mogami departed Brunei on what would be her last operation.
The battleship Fuso and Mogami under air attack, October 24th, 1944.
Mogami met her end on October 25th, 1944 in the Battle of Surigao Strait. The southern thrust of the IJN's attempt to smash the American beachheads on the island of Leyte was split into two groups. In the van of the Southern Force (Force C) were two old battleships,
Fuso and
Yamashiro, the heavy cruiser
Mogami, and four destroyers (
Michishio,
Asagumo,
Yamagumo, and
Shigure).
The Second Striking Force consisted of two heavy cruisers (
Nachi and
Ashigara), one light cruiser (
Abukuma), and eleven destroyers. Overall command was given to Vice Admiral Shoji Nishimura, with
Yamashiro as his flagship. The Second Striking Force was directly commanded by Vice Admiral Kiyohide Shima abord
Nachi, they departed later than Force C and would transit the strait about 40 miles behind the van.
Arrayed against them was a force of six American battleships, most of which were battleships repaired from the damage they'd sustained at Pearl Harbor, three heavy cruisers, five light cruisers, twenty-nine destroyers, and thirty-nine PT boats under the overall command of Rear Admiral Jesse B. Oldendorf.
Over the course of October 24th, the Japanese force had come under air attack, with
Mogami suffering minor damage from near misses and strafing. But the fiercest combat wouldn't be until well after the sun set.
Just after midnight (0018-0035 hours)
Mogami came under torpedo attack from PT boats, none of which connected. At 0105 she was struck by a dud 6'' shell fired by a
Fuso, which failed to identify her in the darkness, killing three men. Then she took station astern of
Fuso.
The formation would be under sporadic torpedo attack from PT boats until 0300, when DesRons 24, 54 and 56 launched their own torpedoes. These attacks did serious damage, sinking the destroyer
Yamagumo, crippling
Michishio and
Asagumo, and hitting
Fuso and
Yamashiro. These hits would doom
Fuso before she ever came into range of the American battleships, and she would explode and sink around 0345.
Painting of Fuso and Yamashiro firing their guns in the evening.
At 0342 the USS
Bache (DD-470) engaged
Mogami with her main battery of 5'' guns, scoring several hits. Once in the strait
Mogami turned to port and accelerated to 25 knots, in an effort to bring her torpedoes to bear on the enemy. At 0354
Hutchens and
Daly joined
Bache, scoring several more hits, setting fires, and disabling the rear radio room. These destroyers were misidentified as Japanese, which delayed
Mogami's return fire.
Mogami continued southeast, making smoke and making ready to launch her torpedoes when she came under fire from two heavy cruisers. One 8'' shell hit and disabled the #3 turret, another that hit at 0359 set a fire near the starboard air intakes, which forced the evacuation of the Number Three engine room and the shut down of the outboard screw on the starboard side.
Shortly after 0400, the port side tubes fired four torpedoes towards the American battle line. Then a barrage of 8'' shells, probably from USS
Portland, started to hit home. Two hit the compass bridge and air defense platform on the bridge tower, killing
Mogami's CO (Captain Toma Ryo, posthumously promoted to Rear Admiral), his XO (Captain Hashimoto Uroku), and several other senior officers. Two more shells knock out Engine Rooms One and Four, leaving only Engine Room Two and the portside outboard screw operational.
LtCdr Arai Giichiro,
Mogami's gunnery officer, took the conn and ordered the stricken cruiser to withdraw. She only managed 8 knots and was steered by hand and with the sole remaining engine.
At 0415, 11 miles southwest of Hibuson Island, lookouts spotted the heavy cruiser
Nachi, flagship of Vice-Admiral Shima Kiyohide.
In the confusion of the battle and darkness, the crew on
Nachi didn't realize that
Mogami was still underway, and the two ships collided at around 0420. The impact tore a hole above the waterline on
Mogami's starboard side, near the #1 turret.
Nachi came away far worse, with one AA gun destroyed, and a 15-meter gash in her bow near the chain lockers. With the realization that the van of the Southern Force was all but annihilated, the surviving ships start to withdraw to the southwest.
At 0441,
Mogami manages to get to 14 knots, but the fires reached unlaunched torpedoes and caused them to detonate. Less than five minutes later the last engine room was evacuated, though the turbine continued to run. At 0450 the badly damaged
Asagumo joins
Mogami, and
Ashigara manages to avoid running into
Mogami around 0500.
But the Americans weren't about to let some Japanese warships run without making an effort to pursue them. The heavy cruisers
Louisville,
Portland, and the light cruiser
Denver caught up with
Mogami around 0530. Despite at least ten additional hits amidships, LtCdr Arai managed to steer
Mogami away from the American ships to escape.
From 0600 to 0630
Mogami, with the other surviving warships of the Southern Force managed to drive off several attacks by PT boats, who failed to score any hits on the ships.
VADM Kiyohide ordered
Mogami, limited to 12 knots, and
Akebono to head for Cagayan (on the island of Luzon, at the northern tip of the Philippine islands) or Coron (on the island of Coron, west of the main islands of the Philippines).
But it would not come to pass, starting at 0717 hours American aircraft started to make themselves known. The first attack was beaten off without damage, but at 0902 six Avengers and Five Wildcats from the USS
Ommaney Bay (CVE-79) strike. The Avengers claim five hits, but actually only manage three hits with 500 pounds bombs. But these are enough.
The last turbine is stopped, and uncontrollable fires start from the forward aviation gas tanks. At 1047 the crew depart, and at 1256
Akebono fires a single Type 93 torpedo into
Mogami's port side. The cruiser finally sinks by the bow at 1307, taking 191 sailors and one civilian worker down with her. 700 survivors, 125 of whom are wounded, are rescued by
Akebono.
A map that shows the general location of Mogami's wreck, the strait is the north-south waterway north of Surigao City. Coron would be at least 400 miles away, and Cagayan would be at least a thousand miles away.
The Battle of Surigao Strait was a crushing victory for the American force, all of Force C except the destroyer
Shigure were sunk by the 26th, and most of the ships in the Second Force were sunk by aircraft or submarines in the next few months of the Philippine Campaign.
The Wreck
Mogami is resting upright, but the damage that she sustained on October 25th, 1944 can be seen even on the sonar images.
As usual, the analysis will start from the bow and work to the stern. New additions and photos will be added to their relative position in the analysis.
A large section from the bow was folded back over the top of Turret #1. While there aren't photos of the starboard side, I suspect that this feature of the wreck had its origin in the damage
Nachi inflicted when she rammed
Mogami. After
Mogami sank, the force of the water would be more than able to fold the bow over in this manner.
This photo shows the anchor chain going down into the chain pipe that leads to the chain lockers. The two cylinders on the lower right are part of an apparatus called a bitt. Bitts are used to secure mooring lines, but any rope that was wrapped around them has long since decayed.
This looks to be the bow combing, used to deflect spray from the rest of the gun mounts and other equipment on deck.
Turret Two looks to be mostly intact. The reason that the barrels on the wrecked warships are so often pointed up to their maximum elevation or beyond is because of the deterioration of the elevation systems, and the somewhat breech-heavy design of many guns results in the barrels pointing towards the surface.
Turret Three, which was knocked out in the first few shots from the American cruiser force. Unfortunately, there are no released images that show the damage that was done.
The base of the bridge tower, this is on the level of the commander's quarters, looking from the port side. The cylinder supported by a strut on the top is the bottom of an observation post. The debris on the left side is a platform that once had a pair of twin 13 mm/76 Type 93 machine guns before they were removed during her conversion to a seaplane cruiser.
These guns were Hotchkiss derived, with a close mechanical lineage to the much-maligned 25mm cannon that was so often used by the IJN. Like every other nation, the Japanese determined that even large machine guns weren't suitable for air defense. Even so, they continued to produce these guns by the thousands until the very end of the war.
Slightly higher up the remains of a 1.5-meter navigational rangefinder can be seen on the upper right side of the frame. The observation post is right in the center. In the back is the armored pilothouse, which would be towards the left, and a radio room on the right side.
The compass platform, showing the damage from the 8'' shells that struck that night in October 1944.
Another view that shows the interior of the platform. Aside from the compass, there were also 12 and 18 cm binoculars on this level for target spotting. This level is (5) on the diagram below, the rangefinder and observation posts shown above are (13) and (14) respectively.
As much as I would like to, I cannot provide a full breakdown of what every item on the diagram is, because the book that it's from is in Polish. Since I cannot read Polish, and the online translators that are available are poor at translating the more technical terms, the diagram will have to suffice.
Portland was probably firing armor-piercing shells at
Mogami. The American Mark 19 8'' AP shell weighed 260 pounds and had an explosive filler of 3.64 pounds of Explosive D. Also known as 'Dunnite' (ammonium picrate), this explosive was used by the US Navy because of its resistance to shock detonation, which allowed AP shells to pass through an enemy ship's armor before the fuse detonated the explosives.
Those killed by the hits included
Mogami's commanding officer Captain Toma Ryo, her Executive Officer Captain Hashimoto Uroku, the Navigator LCDR Nakano Nobuyuki, the Communications Officer LT Okubo Takeo, the lookout officer Li (first name and rank unknown), and the Radar, Damage Control, and Assistant Communications officers were also killed.
The 6-meter rangefinder for the main battery, this view is directed from the rear of the rangefinder and the rangefinder tower. This is a 94 Shiki rangefinder tower, which is a somewhat confusing designation.
To keep it simple, the number is the last two digits of the Imperial Calendar Year, which has its origin with the reign of Emperor Jimmu way back in 660 B.C. This particular method started to see use in 1927 A.D., which is the Imperial Year 2587, so a gun or other piece of equipment designed in 1927 would be designated '87 Shiki'.
Based on this, the 94 Shiki tower can be loosely read as 'Model 1934'. This is items (2) and (3) on the diagram of the tower above.
The 95 Shiki (Type 95, Model 1935) fire control tower. This is located atop the 94 Shiki tower and is marked as (1) on the diagram above.
This is the splinter shield for one of
Mogami's twin 40 caliber Type 89 12.7 cm Guns. It is possible that the chunks that are missing from the lower shield are from battle damage since
Mogami did suffer a protracted bombardment from aircraft and the American cruisers.
This photograph of
Mogmai's starboard side in 1943 shows the two twin 12.7cm mounts, as well as 25mm guns, and some of the large number of aircraft located on the stern.
The forward torpedo launcher on the port side. This is a triple mount, and
Mogami had four of them in total. By 1944 she was fitted with reloads of all tubes, for a total of 24 torpedoes available to fire.
The base of the port catapult.
This is what
Mogami's stern looked like in 1943. The monoplanes are Aichi E13A 'Jake' seaplanes, they first flew in 1939 and were a common scout airplane in the IJN for the entire war, with more than 1,400 being produced. Interestingly, some of them remained in service with the
French from 1945 to 1947 during the First Indochina War.
The biplanes are Mitsubishi F1M 'Pete' seaplanes. These were the last biplane operated by the IJN, and nearly a thousand were built by 1944 when production stopped. They were versatile aircraft, being used as fighters, bombers, scouts, and towards the end of the war, as kamikaze aircraft.
The rear port side torpedo tubes. Since the port side torpedo tubes aren't demolished, it seems probable that the fires and torpedoes that exploded were more on the starboard side of the ship.
A single 25mm cannon, one of the single mounts added during her last refit. This photo also shows how the aircraft deck has caved in. Large portions of it were made of wood, which has long since rotted away.
The port side rudder, with some of the loose debris that has fallen away from the stern. The very end of Mogami is in bad shape, possibly from being crushed under the pressure of the ocean before the interior could fully flood.
This is the very end of the stern, showing more of the extensive damage to the area.
Starboard side rudder and the tip of the inboard starboard side screw.
Another sonar image that shows some of the extensive damage to the ends of
Mogami.
Unfortunately, there probably won't be more photos or video documenting
Mogami in the near future. As the ROV made the turn around the stern, there was an electrical fault that force the
Petrel to reel it back in, and they had to move away from the wreck by the time they were able to get it repaired.
Sources:
General History and Images
RV Petrel Facebook page
Mogami-class Heavy Cruiser | Nihon Kaigun - Information on the
Mogami class as a whole.
https://ww2db.com/ship_spec.php?ship_id=38 - Information on the class as a whole, and photographs.
Yamato class genesis - Information on the design teams of the IJN pre-WWII.
Imperial Cruisers - Information on the history and movements of
Mogami.
Leyte Campaign | Nihon Kaigun - Battle of Surigao Strait force composition.
Orders of Battle - Battle of Surigao Strait - Battles of the Pacific - World War II - NavWeaps - Battle of Surigao Strait force composition.
Imperial Japanese Navy Mysteries - Information on the collision between
Nachi and
Mogami during the battle.
http://www.combinedfleet.com/atully06.htm#fusomap1 - Information on the fates of
Fuso and
Yamashiro at Surigao Strait.
http://www.combinedfleet.com/radar.htm - Information on Japanese wartime radar sets.
Shattered Sword: The Untold Story of the Battle of Midway, Parshall, Johnathan, and Tully, Anthony. 2005.
Japonskie krazowniki typu Mogami, Malinowski, Jaroslaw. 1994.
Armament and Equipment
http://www.navweaps.com/Weapons/WNJAP_8-50_3ns.php -
Mogami's 203mm guns.
http://www.navweaps.com/Weapons/WNUS_8-55_mk9.php - American 203mm guns and shells.
http://www.navweaps.com/Weapons/WNJAP_61-60_3ns.php -
Mogami's 155mm guns.
http://www.navweaps.com/Weapons/WNJAP_5-40_t89.php - Japanese 127mm guns.
http://www.navweaps.com/Weapons/WNJAP_25mm-60_mg.php - Japanese 25mm guns.
http://www.navweaps.com/Weapons/WNJAP_13mm-76_mg.php - Japanese 13mm guns.
http://www.navweaps.com/Weapons/Gun_Data.php - Information on Japanese equipment designation schemes.
http://navypedia.org/ships/japan/jap_cr_mogami.htm - Information on specifications of the class, and the changes that were done during refits.
1930s 1940s History IJN Navy RV Petrel The Pacific WWII
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MJSpockJuly 13, 2021 at 8:29 AM
Really excellent website
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