Failure Knowledge Database / 100 Selected Cases

The 4th Fleet incident
Sep. 26th,1935, Offshore east of Sanriku in the Pacific Ocean
KOBAYASHI, Hideo (Tokyo Institute of Technology)(Summary)
On Sept ember 2 6th, 19 35, the Japa nese 4th Fle et en countered an a bnormal ty phoon w hile t hey w ere
conducting maneuvers 250 m iles east of Sanriku coast in the Pacific Ocean. The ty phoon damaged many
vessels seriously and t ook a heavy toll of human lives. The m ost serious d amage to these vessels was thebreaking of f of the bow p ortions of t he H atsuyuki and t he Yugiri, w hich w ere Japanese Sp ecial-Class
Destroyers.
The 4th Fle et inc ident o ccurred because the flee t w as confro nted with w aves l arge than they h ad
expected. The ca use of this incident was invest igated and s ome new facts

were dis covered. As aconsequence, these vesse ls were reinforced and were t hereafter ab le to fulf ill their missions witho ut a ny
further problems.
1. Component
Vessels of the 4th Fleet, especially the two Special-Class Destroyers Hatsuyuki (Fig. 1) and Yugiri (Fig.
2).
2. Event
The Japanese Nav y's l arge-scale m aneuver in 19 35 was pu t in to op eration b etween th e S tanding
Combined Fleet (Blue Fleet) and the Red Fleet. The Blue Fleet consisted of the 1st and 2nd fleets. The Red
Fleet, which contained the 4th Fleet, was assembled temporarily. The maneuver started in July, and it was
supposed t o end after th ecompetition between t he Red and B lue Fleets in t he lat e Se ptember. T wo
remodeled ba ttleships (Yamashiro, Haruna), and n ew and powerful cru isers (Mog ami Class, Hatsuh aru
Class) participated in this maneuver, and therefore a considerable result was expected.
In the late September, the Red Fleet crossed over the Tsugaru Straits and cr uised toward the east. The
Red fleet was expected to advance to the east of Honshu Island and reach position for the battle against theBlue fleet at there. However, the weather became extraordinary rough fro m 14:00 on Septem ber 26th, due
to a typhoon. During the storm, the bridges of two destroyers (Hatsuyuki, Yugiri) were knocked off by huge
waves. In addition to this, the bridge of the destroyer Mutsu was smashed, the front side of the bridge of theaircraft carrier Ryujo was damaged, aircraft carrier H osho plunged into waves and crashed her deck so it
became uncontrollable, and all of the other vessels suffered slight or heavy damages. Consequently the Red
fleet abandoned its maneuver. The vessels in the fleets except for the heavily damaged vessels conducted amaneuver off Sanriku, and after that maneuver, they gathered off Shinagawa in Tokyo bay. At the end of the
maneuver, on October 7th, a review to ok place on the Hiei, which was the o bserving vess el of th e
maneuver, in the presence of the president of the headquarters Hushiminomiya.
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Failure Knowledge Database / 100 Selected Cases

The 4th Fleet incident was unprecedented and so serious that the authorities strictly concealed the facts(in addition, Japan withdrew from the L ondon Naval Conference the next year). It w as the first time thatthe hull of a vessel was knocked off since the British destroyer Cobra (370 tons) was split in half during her
first cruise in 1899. This incident, together with the capsize of torpedo boat Tomozuru, called into doubt thequality of the Japanese Navy's shipbuilding technologies.
According t o the i nvestigation, the pri ncipal c ause o f this incident was a lack of stre ngth of th eSpecial-Class d estroyers. Although th e vessels had op erated fo r sev en years wi thout an y p roblems, t heinvestigators concluded that their strength was ins ufficient. As a res ult, it was decided that reinforcement
was needed for the cruisers, destroyers and even aircraft carriers. As a result of the detailed investigation, it
became clear that the Special-Class destroyers were damaged because of the deterioration of strength after
several years of operat ion. However, these facts were not considered carefully, a nd th ey were treate d aspolitical matters instead of technical ones. That was one of the reasons why the 4th Fleet incident could not
be prevented.
In the 1930's, welding was used for assembling many newly built vessels. Although welding was not theimmediate cause of this incident, ships that were constructed using welding for assembling the main parts
often proved not to have enough strength.
The 4th Fleet incident occurred because the vessels in the fleet were confronted by unexpectedly large
waves. An intensive investigation re vealed se veral ne w facts. As t he resu lt, al l of th e v essels were
reinforced and were able to fulfill their missions without failure since then. In this case, shipbuilders can beconsidered to be responsible for the incident.The 4th Fleet incident and the case of the Tomozuru, were theworst scanda ls in the ei ghty years of th e Jap anese N avy's history. Just b efore the crisis in 1936, m any
people do ubted the Ja panese N avy's co mbat p ower as a result of the se inc idents. However, t hese dou bts
were completely removed by extraordinary efforts and proper treatment of the persons concerned.
3. Course
On O ctober 10th, 1935, a com mission of in quiry w as form ed. A dmiral K ichisaburo N omura w as
appointed as the commission chairman. Vice Admiral Isoroku Yamamoto and Rear Admiral Mineichi Koga
(both of them were later to hold the position of commander-in-chief of the Japanese Grand-Fleet) were also
members of the committee. In the cases of the Hatsuyuki and the Yugiri, a hu ge wave caused a pitchingmotion of the vessels to occur. Then wrinkles appeared on the steel board of the front decks of the vessels,
and t he decks bega n t o bu ckle. The c ommittee co ncluded t hat as th e vessels' pitc hing m otion occurredagain and again, wrinkles become cracks and finally divided the vessel into two parts (Fig. 3). In addition
to the wrinkles on t he front desks, both of the v essels had wrinkles also on the quarterdeck, and wrinkles
could even be found on some of the other vessels that might cause parts of the vessels to break off.
On July 19 35, Speci al-Class D estroyers, incl uding t he Mura kumo, had cr uised at hi gh s peed in aheaving sea near Tokyo Bay before th is incident, and the same type of slight wrinkles were found in the
Murakumo. One m ajor who invest igated the cause of the wrinkles in the Murakumo at Yokosuka came tothe conclusion that the primary factor l eading to t he occurrence of the wrinkles was a seri ous lack of the2

Failure Knowledge Database / 100 Selected Cases

vessel's strength. He reported that they must reconsider the participation of these Special-Class Destroyers
in the maneuver. However, his superior officer rejected his proposal for fear that if the problem came to thesurface just before the maneuver then it might be perceived as a complete blunder of the authorities, so they
reinforced the Muraku mo only. The 4th Fleet incident occurred just after this case, but the defects of thesevessels had already existed before the incident.
On O ctober 21st, 1 935, t he Ja panese Navy establis hed a speci al investi gative com mittee for the
improvement of t he efficiency of naval v essels. Admiral Se izo K obayashi became th e chairman, a nd th ecommittee went into action to find out the cause of the incident and decide the most effective measures todeal with the cause. Investigations and discussion continued night and day for fi ve months, and finally afull and detailed report was made in April 1936.
The 4th Fleet incident, as well as the capsize of the torpedo boat Tomozuru, was such a serious example
of a case that they had never experienced before that authorities decided to completely conceal the facts.
4. Cause
Although it turned out to be true that the cause of the 4th Fleet incident was the lack of strength of theSpecial-Class Destroyers, all the destroyers of this class had been in commission without any problems forseven years. Since these vessels that had been thought to be perfect were acknowledged as defective, all thecruisers, destroyers, and even air carriers that were constructed later than these vessels had to be reinforced
immediately. A sim ilar case ha ppened with ty pes of vessels that were hea vier than t he designs or had
become rem arkably hea vy as a resul t of so me altera tions. T hey i nvestigated t he situation re garding t heSpecial-Class D estroyers in deta il a nd fo und th at m any problem s cause d by the defect ap peared sev eral
years after th e vesse ls were co nstructed. However , these facts wer e not c onsidered seri ously, and som e
political matters blocked technical investigations. As a result, the 4th Fleet incident occurred.
Additionally, most of th e bodies of newly constr ucted vessels w ere w elded a t t hat tim e. A s t heinvestigation went on, vessels whose bodies were welded proved to have reduced body strength (although
this fact was not the direct cause of the incident).
5. Immediate Action
Figure 5 shows the definition of the wave length T and the wave height H. During the heavy weather,
the heavy Cruiser Nachi, one of the vessels of the 4th Fleet, recorded that the wave length T was 100~150m
and the wave height H was 10~15m. The ratio of T to H was approximately 10. The battleships of the 4th
Fleet recorded the same ratio, but a torpedo boat in another area reported that T was 200m and H was 15m.
In t hat c ase the ra tio was about 13. 3. This wa ve was no t a chopping wave whi ch th e Sp ecial-Class
Destroyers drove into; it was just a result of an observation of a big wave. Based on these records and otherinvestigations, in vestigate committee cam e to t he c onclusion t hat i n the s ea near J apan, when the wi nd
velocity is more than 70m/s the average wave length T is 500m and the average wave height H is 23~26m,
when t he w ind ve locity is approximately 50 m /s, T is 28 0m and H i s 15~ 18m (these co nditions usua lly
occur twice a y ear) an d wh en the win d velocity is 4 0m/s, T is 180m and H is 11~14m (these co nditions
occur about ten times a y ear). According to this report, the ratio of T to H ra nged between 10~13, and it
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Failure Knowledge Database / 100 Selected Cases

was almost always around 10 during a typhoon.
In this i nvestigation, m any records of t he H ydrographic D epartment an d o ther nati onal arc hives
referring to sea waves were consulted. However, it is difficult to observe sea waves accurately, and so few
reports are reliable.
Shipbuilders in those days used the following standard for the calculation of the vessel's strength: theratio of T to H is 2 0 and T is not longer than the length of the vessel. It can be calculated that the torqueapplied to a v essel is l argest whe n the wave le ngth a nd t he v essel's len gth are t he same (this ca lculation
treats the sha pe of t he wa ve as a trochoidal wa ve). This ca lculation re sult wa s u sed un iversally. The
bending stres s cur ves based on t his m ethod m ade it easy t o c alculate t he bending stress on each cr oss
section of the vessel in order to decide the size and the structure method of the reinforcement. The problem
was the value of the bending stress itself because it was required to be far less than that of the failure stress.
The T to H ratio of the wave that the 4th Fleet encountered was much higher than the standard ratio of
20. H owever, this is a rel atively c ommon phenomenon i n t he se as near Ja pan. Thus t he conventional
method to ca lculate the pe rmissible range of th e be nding stress nee ded to be reconsidered carefully.
Moreover, the strength of the vessel must be calculated even in the case that the T to H ratio is 10.
The c ause of the 4th Fle et incident w as obviously t he im perfection in t he s tructure of t he J apanese
Navy's vessels. However, it was found that sometimes waves were much larger than had been previously
observed, a nd the authorities de cided to strict ly co nceal the meteorological si tuation itself d uring t heincident in addition to the cause and the measures of the incident.
Some of the other Special-Class Destroyers also had wrinkles on their foredecks that might have caused
the breaking off of parts of the vessel, and some of them even had wrinkles on their quarterdecks.
The cruiser Mogami had so me wrinkles on the welded bow since the time that it was constructed, but
after the incident the wrinkles became enlarged and the main structure started to break down. During t hestorm, the Mogami made strange noises near the main battery and the bow vibrated terribly, causing all of
the sailors to become terror-stricken. The submarine depot ship Taigei, whose weight exceeded 10,000 tons,
inclined more than 50 degrees, and seawater leaked into the vessel. As a resul t, one of the electric motors
was broken, and the vessel became temporally uncontrollable. Like the Mogami, the Taigei also had somewrinkles on s ome of the pl ates on t he deck i n front o f the bri dge. Some w alls aroun d th e bri dge of theaircraft carrier Ryujo were crushed by rough waves since the foredeck was slightly low. Finally, the rivetsin the middle of the heavy cruiser Myoko were loosened.
Huge waves destroyed a lot of rigs as well as vessels themselves. In summary, all of the vessels in thestorm were damaged to some degree.
The stre ngth of th e Spe cial-Class Destroyers was calc ulated caref ully, a nd as a r esult t he m aximum
stress ap plied by n ormal waves was not s o h igh if th e v essel w as co nstructed ac cording to t he plan.
However, t he w eight w as increased considerably in comparison t o th e ori ginal pla n, a nd s ome otheradaptations also altered the weight of the vessels. In normal vessels, the applied stress on the front and backof the vessel is decre ased remarkably be cause lo ngitudinal ste el rei nforcements s hare t he exter nal forc e.
However, the Special-Class Destroyer used relatively thin reinforcement at the front and the back, so the4Failure Knowledge Database / 100 Selected Cases

stresses on the vessel's front and back became same level as those at middle. The shipbuilders thought that
this might contribute to the reduction of the weight of the vessel. When the vessel encountered waves thatwere larger than expected the stress on the middle part of the vessel was increased, although the proportionof the stress increase on the front and back parts varied between each vessels depending on the distributionof t he reserve buoyancy a nd t he flota ge. The stress of the Special-Class Destroy er in creased 45% o n the
middle part and 69% on the front part when the T to H ratio changed from 20 to 10. This stress was mainly
due to the compressive stress that occurs when the vessel is located between waves (subbing); the stress on
the top of a wave (hogging) was not so large as the subbing one. Fig. 6 shows examples of su bbing andhogging. In other words, the Special-Class Destroyer was constructed without careful consideration of thestress distribution in order to reduce her weight.
As a result of the a bove considerations, the S pecial-Class D estroyer w as cons tructed t o have go od
seaworthiness, but the foredeck was higher by one step than other vessels. As a resul t, a large compressive
stress was applied on the deck when the vessel encountered a big wave. Although shipbuilders considered
the perm issible l imitation of t he b uckling ag ainst th e c ompressive s tress carefully, s ome of theconsiderations were inappropriate. These issues contributed to the cause of the breaking off of the parts ofthe de stroyers du e to the rep eated co mpressive stress. That is to say , it was clear that the thinness of thesteel plates and the heights of the waves were the causes of the 4th Fleet incident. And detailed calculationsof all other vessels' strength were done as same way.
6. Countermeasure
It was not so difficult to find the way of reinforcement of the vessel by calculating the applied stressesof the vessels in severe conditions. However, the reinforcement of existing vessels is much different fromchanging the struct ure of a new vess el. M oreover, the rei nforcement must af fect t he ot her vesse l's
performance as lit tle as possible. T ime cons uming works for reinforcem ent could e ndanger N ational
defense at that time, and of course the government wanted to keep costs as low as possible. However, thesituation was so serious that the Ja panese Navy took extraordinary bold and thorough measures to repair
the situation.
Most of the small vessels went into dock and almost all of their plates and decks were stripped. Bridges
were separated from the bodies of the vessels, and sustained by logs then all of the required reinforcement
was conducted.
Although wel ding a t th at time was not well understood, sh ipbuilders o verused th is in complete

technology. D esigning and methods of c onstructing w elded s tructures are insufficient in many regards .
Consequently, welding between parts critical to the strength of a vessel was discontinued and rivets wereused again.
With th ese co untermeasures an d through great efforts o f the p eople c oncerned, the reinf orced vessels
were abl e t o accomplish t heir missions without any furt her problems related to strength defi ciency sincethen.
This incident, together with the case of the Tomozuru, was com pletely settled under the leadership of5

Failure Knowledge Database / 100 Selected Cases

Rear Admiral Keiji Fukuda (he w as promoted to Technical Vice Admiral later) and Prof. Yuzuru Hiraga,dean of th e F aculty of E ngineering a t t he U niversity of Tokyo. Many tec hnicians fro m other dockyards
assisted them in their investigations and calculations. Most of the reinforcement was finished by the end of
1936, and all the reinforcement was completed at the end of 1938.
7. Knowledge
Unexpected and unusual r ough wea ther tau ght t hat t echnologies were stil l i ncomplete. Due to thislesson, shipbuilders nowadays have a cer tain confidence base d on preci ous e xperience ab out a vessel' s
strength. We should make the most of this experience in order to give our respect for the victims of the 4th
Fleet incident.
8. Background
One of the reasons that the strength of these vessels became weakened was the demand for an increaseof each individual vessel's combat power within the limited vessel's structural mass because the Conference
on the Limitation of Arm ament in Washington limited the total weight of wh ole vessels. This conference
was held by the U.S.A, the British Empire, France, Italy, and Japan in November 1921.
Following t his co nference, the Lo ndon N aval C onference also l imited the num ber of s upport vessels
and submarines after m any twists and turns. In this treaty, Japan appeared to have had her demands fromthe U .S.A an d t he Bri tish Em pire fulfi lled, but in f act t he U .S.A ga ined a n a dvantage o ver Japa n inconstructing support vessels under the restriction. Thus the Japanese naval vessels had to mount many guns
at the cost of their structural strength, which led to the exposure of major defects. The 4th Fleet incident
forces us to recognize that inconsistency between policy and technology will cause unexpected tragedy.
9. Sequel
The U.S. Navy's 3rd fleet, which was under t he command of Admiral Halsey, was heavily damaged by
two typhoons during the Pacific War.
On December 18th, 1944, one of the units of the 3rd fleet encountered a rough typhoon near Philippine.
Three destroyers were caps ized an d sank; 18 vessels w ere badly damaged an d 9 w ere slightly damaged;
and 183 aircrafts and over 700 lives were lost. The fact that the fuel tanks of the three sunken destroyers
were all empty worsened the situation.
The second typhoon encounter took place on the sea near Kyushu on Jun e 4th and 5t h, 1945. General
Halsey wanted to attack Kyusyu to halt the Kamikaze attacks, so some units moved northward and carriedout a n a ttack on Ju ne 2nd, b ut the m ilitary resul ts were n ot suf ficient. After the at tack, an e normous
typhoon ap proached t he se a area ne ar K yusyu and O kinawa a nd heavily d amaged som e uni ts. The 3rd
fleet's four battleships, two aircr aft carriers, two light aircr aft carriers, fo ur es cort carri ers, three heavy
cruisers, four light cruisers, and seventeen other vessels were seriously damaged, and most of th e aircraft
were destroyed.
The 3rd fl eet was unfort unate, b ut i t is d oubtful th at t he U .S. N avy had c onsidered t hat ty phoons or
storms might damage the v essels (of course the ca use of th e 4 th Fle et i ncident w as the to p se cret of the6

Failure Knowledge Database / 100 Selected Cases

Japanese Navy, and the U.S. Navy could not have know it). In contrast, no vessels in the Japanese Navy
were dam aged d ue t o e ncountering a typhoon af ter t he 4t h Flee t i ncident. I n m ilitary situa tions, sharin g
knowledge of failure cases between enemy nations cannot be realized.
10. Primary Scenario
01.Organizational Problems
02. Inflexible Management Structure
03. Acceptance of Unreasonable Demands
04. Unknown Cause
05. Occurrence of Abnormal Phenomenon
0 6. Typhoon
07. Insufficient Analysis or Research
08. Insufficient Prior Research
09. Insufficient Judgments/Rethinking
10. Planning and Design
11. Poor Planning
12. Bad Design
13. Warships/Vessels
14. Lack of Vessel's Strength
15. Usage
16. Operation/Use
17. Cruise
18. Possible Damage
19. Potential Hazard
20. Huge Wave
21. Failure
22. Deformation
23. Buckling
24. Loss to Organization
25. Social Loss
26.Defense Deterioration

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Failure Knowledge Database / 100 Selected Cases

Fig. 1 Destroyer Hatsuyuki.

Fig. 2 Destroyer Yugiri.

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Failure Knowledge Database / 100 Selected Cases

Fig. 3

Damages of Destroyer Hatsuyuki.

Fig. 4

Damages of Destroyer Mutsuki.

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Fig. 5 Definition of Wave Length(T) and Wave Height(H).

Sagging

Hogging
Fig. 6 Subbing and Hogging.

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