4th Fleet ( Imperial Japanese Navy ) The was a fleet designation of the Imperial Japanese Navy . The Fourth Fleet designation was used during three separate periods . The initial designation was for a group of ships that were assigned to work together during the Russo - Japanese conflict and the period of its immediate aftermath . The second time the designation was used was during the Sino - Japanese conflict , and the third time was as a South Pacific area of command during the middle of the Pacific War . History . Russo - Japanese War . First established on June 14 , 1905 , the 4th Fleet was created after the Battle of Tsushima in the Russo - Japanese War specifically to support and cover the landings of Japanese forces in Sakhalin . Afterwards , it was sent to the United States with the Japanese delegation negotiating the Treaty of Portsmouth ending the war , and was disbanded on December 20 , 1905 . The Fourth Fleet Incident . While participating in war game maneuvers in 1935 the Fourth Fleet became caught in extremely foul weather . The weather continued to deteriorate and by 26 September had reached typhoon status . Two of the newer , large " Special Type " destroyers , the " Hatsuyuki " and the " Yugiri " , had their bows torn away by the heavy seas . A number of recently built heavy cruisers also suffered significant structural damage . The " Myoko " , the " Mogami " and the submarine tender " Taigei " developed serious cracks in their hulls , and the light aircraft - carriers " Hōshō " and " Ryujo " suffered damage to their flight decks and superstructure , with the " Ryujo " also having her hangar section flooded . The minelayer " Itsukushima " suffered damage that required several months for extensive repairs , necessitating a near complete rebuild . Nearly all the fleet ' s destroyers suffered damage to their superstructures , and fifty - four crewmen were lost , swept overboard or killed outright . The Japanese Admiralty held a hearing on the damage suffered by Fourth Fleet in the storm , resulting in recommendations for changes on Japanese warship design and construction . A number of new designs that used heavier guns and taller superstructures were found to be top heavy , and efforts were made to stabilize these ships by reducing weight above the waterline . In addition cracks in the hulls of the new cruisers indicated the recently adopted practice of electric welding hull seams was suspect , and the practice was canceled on all new Japanese warship construction . The event was kept a secret from the public . A similar event occurred to the US Third Fleet some nine years later in December 1944 when it faced Typhoon Cobra . Second Sino - Japanese War . On October 20 , 1937 , the 4th Fleet was resurrected as part of the emergency reinforcement program for the China Area Fleet after the North China Incident of 1937 . The new 4th fleet was based out of Tsingtao and assigned to patrol the Bohai Sea and the East China Sea regions . However , unlike the IJN 5th Fleet , the 4th Fleet was never in actual combat . On November 15 , 1939 , the 4th Fleet was absorbed into the 3rd China Expeditionary Fleet under the overall aegis of the China Area Fleet . Although most of its ships were released for service with the Combined Fleet in the Pacific War a year later , most of the staff for the 4th Fleet remained in China , and were assigned to the Tsingtao Base Force for the duration of the war . Pacific War . On the same date at that the 4th Fleet was absorbed into the China Area Fleet , a new 4th Fleet was created to provide administrative control over Japanese naval forces in the Japanese - held island territories of the South Pacific ( Caroline Islands , Marshall Islands , Mariana Islands , Palau ) . This third IJN 4th Fleet came under the aegis of the Combined Fleet on November 15 , 1940 . The operational name of this fleet was the South Seas Force . With the start of hostilities against the United States , the 4th Fleet was based out of Truk , with a secondary base at Kwajalein . After initial Japanese successes , additional bases were established in the southern Philippines , Guam , Wake Island , Gilbert Islands , eastern New Guinea , Bismarck Archipelago and the Solomon Islands . After the Battle of the Coral Sea , the area covered by the 4th Fleet was reduced to an “ inner core ” of Japanese possessions , while the new IJN 8th Fleet was assigned to confront the advancing American forces in the Solomon Islands and New Guinea . However , in November 1943 , the Americans attacked the Gilbert Islands and captured the major naval base of Tarawa , which brought the 4th Fleet and its various garrison forces back into the front lines of combat . The Americans continued to advance through the Gilbert and Marshall Islands in early 1944 , capturing the IJN 4th Fleet HQ in Truk in February , and pushing the surviving units back to Palau , which also proved vulnerable to air attack . In March 1944 , the IJN 4th Fleet came under operational control of the Central Pacific Area Fleet based in Saipan . It effectively ceased to exist with the fall of Saipan to American forces . Commanders of the 4th Fleet .