was the highest rank in the prewar Imperial Japanese Navy

Imperial Japanese Navy

The Imperial Japanese Navy was the navy of the Empire of Japan from 1869 until 1947, when it was dissolved following Japan's constitutional renunciation of the use of force as a means of settling international disputes...

. The term gensui was used for both the Navy and the Imperial Japanese Army

Imperial Japanese Army

-Foundation:During the Meiji Restoration, the military forces loyal to the Emperor were samurai drawn primarily from the loyalist feudal domains of Satsuma and Chōshū...

, and was a largely honorific title awarded for extremely meritorious service to the Emperor

Emperor of Japan

The Emperor of Japan is, according to the 1947 Constitution of Japan, "the symbol of the state and of the unity of the people." He is a ceremonial figurehead under a form of constitutional monarchy and is head of the Japanese Imperial Family with functions as head of state. He is also the highest...

. In the Meiji period

Meiji period

The , also known as the Meiji era, is a Japanese era which extended from September 1868 through July 1912. This period represents the first half of the Empire of Japan.- Meiji Restoration and the emperor :...

, the title was awarded to 5 generals and 3 admirals. In the Taishō period

Taisho period

The , or Taishō era, is a period in the history of Japan dating from July 30, 1912 to December 25, 1926, coinciding with the reign of the Taishō Emperor. The health of the new emperor was weak, which prompted the shift in political power from the old oligarchic group of elder statesmen to the Diet...

 it was awarded to 6 generals and 6 admirals, and in the Shōwa period

Showa period

The , or Shōwa era, is the period of Japanese history corresponding to the reign of the Shōwa Emperor, Hirohito, from December 25, 1926 through January 7, 1989.The Shōwa period was longer than the reign of any previous Japanese emperor...

 it was awarded to 6 generals and 4 admirals. This rank is similar to fleet admiral.

Note that several were promoted the same year they died - these were posthumous promotions.

	Fleet Admiral !! Name!!(Birth-Death)!! From
1	20 January 1898	Marquis Saigo Tsugumichi	(1843-1902)	Kagoshima
2	31 January 1906	Count Itoh Sukeyuki Itoh Sukeyuki - Notes :...	(1843-1914)	Kagoshima
3	31 October 1911	Viscount Inoue Yoshika Inoue Yoshika - Notes :...	(1845-1929)	Kagoshima
4	21 April 1913	Marquis Togo Heihachiro Togo Heihachiro Fleet Admiral Marquis was a Fleet Admiral in the Imperial Japanese Navy and one of Japan's greatest naval heroes. He was termed by Western journalists as "the Nelson of the East".-Early life:...	(1847-1934)	Kagoshima
5	7 July 1913	Prince Arisugawa Takehito	(1862-1913)	Imperial Family
6	26 May 1917	Baron Goro Ijuin	(1852-1921)	Kagoshima
7	27 June 1922	Prince Higashifushimi Yorihito Prince Higashifushimi Yorihito was the second head of the Higashifushimi-no-miya, an ōke cadet branch of the Japanese imperial family.-Early life:Born on September 19, 1867, as seventeenth son of Prince Fushimi Kuniye, head of the Fushimi-no-miya, one of the shinnōke branches of the Imperial Family of Japan, which were...	(1867-1922)	Imperial Family
8	8 January 1923	Baron Hayao Shimamura	(1858-1923)	Kochi Kochi Prefecture is a prefecture of Japan located on the south coast of Shikoku. The capital is the city of Kōchi.- History :Prior to the Meiji Restoration, Kōchi was known as Tosa Province and was controlled by the Chosokabe clan in the Sengoku period and the Yamauchi family during the Edo period.- Geography...
9	24 August 1923	Baron Tomozaburo Kato Kato Tomosaburo Viscount was a career officer in the Imperial Japanese Navy, cabinet minister, and Prime Minister of Japan from 12 June 1922 to 24 August 1923.-Biography:...	(1861-1923)	Hiroshima Hiroshima is the capital of Hiroshima Prefecture, and the largest city in the Chūgoku region of western Honshu, the largest island of Japan. It became best known as the first city in history to be destroyed by a nuclear weapon when the United States Army Air Forces dropped an atomic bomb on it at 8:15 A.M...
10	27 May 1932	Prince Fushimi Hiroyasu Prince Fushimi Hiroyasu was a scion of the Japanese imperial family and was a career naval officer who served as chief of staff of the Imperial Japanese Navy from 1932 to 1941.-Early life:...	(1876-1946)	Imperial Family
11	18 April 1943	Isoroku Yamamoto Isoroku Yamamoto was a Japanese Naval Marshal General and the commander-in-chief of the Combined Fleet during World War II, a graduate of the Imperial Japanese Naval Academy and a student of Harvard University ....	(1884-1943)	Niigata Niigata Prefecture is a prefecture of Japan located on the island of Honshū on the coast of the Sea of Japan. The capital is the city of Niigata. The name "Niigata" literally means "new lagoon".- History :...
12	21 June 1943	Osami Nagano	(1884-1947)	Kochi Kochi Prefecture is a prefecture of Japan located on the south coast of Shikoku. The capital is the city of Kōchi.- History :Prior to the Meiji Restoration, Kōchi was known as Tosa Province and was controlled by the Chosokabe clan in the Sengoku period and the Yamauchi family during the Edo period.- Geography...
13	31 March 1944	Mineichi Koga Mineichi Koga - Notes :...	(1885-1944)	Saga Saga Prefecture is located in the northwest part of the island of Kyūshū, Japan. It touches both the Sea of Japan and the Ariake Sea. The western part of the prefecture is a region famous for producing ceramics and porcelain, particularly the towns of Karatsu, Imari, and Arita...