270px, No.2 Kaiho（1988） 270px, No.3 Kaiho（1983） 270px, Kenzaki Battery（2010） was the name of a group of coastal fortifications built to guard the entrance to

Tokyo Bay is a bay located in the southern Kantō region of Japan, and spans the coasts of Tokyo, Kanagawa Prefecture, and Chiba Prefecture. Tokyo Bay is connected to the Pacific Ocean by the Uraga Channel. The Tokyo Bay region is both the most populous ...

and thus the city of

Tokyo Tokyo (; ja, 東京, , ), officially the Tokyo Metropolis ( ja, 東京都, label=none, ), is the capital and largest city of Japan. Formerly known as Edo, its metropolitan area () is the most populous in the world, with an estimated 37.468 ...

from attack from the sea. These gun batteries and fortifications ceased to be used after the end of

World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...

History

A series of six island fortresses (''daiba'') constructed in 1853 by

Egawa Hidetatsu was a Japanese Bakufu intendant of the 19th century. Jansen, Hall 1989, p. 815. He was Daikan, in charge of the domains of the Tokugawa shogunate in Izu, Sagami and Kai Provinces during the Bakumatsu period. Jansen, Hall 1989, p. 108. He took ...

for the

Tokugawa shogunate The Tokugawa shogunate (, Japanese 徳川幕府 ''Tokugawa bakufu''), also known as the , was the military government of Japan during the Edo period from 1603 to 1868. Nussbaum, Louis-Frédéric. (2005)"''Tokugawa-jidai''"in ''Japan Encyclopedia ...

in order to protect Edo from attack by sea, the primary threat being Commodore

Matthew Perry Matthew Langford Perry (born August 19, 1969) is an American-Canadian actor. He is best known for his role as Chandler Bing on the NBC television sitcom ''Friends'' (1994–2004). As well as starring in the short-lived television series '' St ...

's Black Ships which had arrived in the same year to force Japan to end its centuries-old national isolation policy Of the originally planned 11 batteries, seven were started construction but only six were ever finished, one of which was the artificial island of

Odaiba today is a large artificial island in Tokyo Bay, Japan, across the Rainbow Bridge from central Tokyo. Odaiba was initially built in this area for defensive purposes in the 1850s. Reclaimed land offshore Shinagawa was dramatically expanded durin ...

After the

Meiji restoration The , referred to at the time as the , and also known as the Meiji Renovation, Revolution, Regeneration, Reform, or Renewal, was a political event that restored practical imperial rule to Japan in 1868 under Emperor Meiji. Although there were ...

, the primary threats to the new

Empire of Japan The also known as the Japanese Empire or Imperial Japan, was a historical nation-state and great power that existed from the Meiji Restoration in 1868 until the enactment of the post-World War II 1947 constitution and subsequent fo ...

were perceived to be

Qing China The Qing dynasty ( ), officially the Great Qing,, was a Manchu people, Manchu-led Dynasties in Chinese history, imperial dynasty of China and the last orthodox dynasty in Chinese history. It emerged from the Later Jin (1616–1636), La ...

Beiyang fleet The Beiyang Fleet (Pei-yang Fleet; , alternatively Northern Seas Fleet) was one of the four modernized Chinese navies in the late Qing dynasty. Among the four, the Beiyang Fleet was particularly sponsored by Li Hongzhang, one of the most trust ...

, followed by the

Russian Empire The Russian Empire was an empire and the final period of the Russian monarchy from 1721 to 1917, ruling across large parts of Eurasia. It succeeded the Tsardom of Russia following the Treaty of Nystad, which ended the Great Northern War. ...

's Pacific Fleet. The

Meiji government The was the government that was formed by politicians of the Satsuma Domain and Chōshū Domain in the 1860s. The Meiji government was the early government of the Empire of Japan. Politicians of the Meiji government were known as the Meiji o ...

ordered the construction of a new set of coastal fortifications starting in 1884. The main facilities were constructed on the western coast of the

Boso Peninsula Boso may refer to: People * Boso of Provence (850–887), Frankish nobleman and king * Boso the Elder (c. 800–855), a Frank from the Bosonid dynasty *Boso, Margrave of Tuscany (885–936), Italian nobleman * Boso II of Arles (d. 967), Frankish co ...

from Cape Susaki in

Tateyama Tateyama may refer to: People with the surname * Midori Tateyama, Japanese writer * Shohei Tateyama (born 1981), Japanese baseball player * Yoshinori Tateyama (born 1975), Japanese baseball player * Homarefuji Yoshiyuki (born 1985), Japanese su ...

to Cape Futtsu in

Futtsu 260px, Futtsu City Hall is a city located in Chiba Prefecture, Japan. , the city had an estimated population of 42,476 in 18,115 households and a population density of 210 persons per km². The total area of the city is . Geography Futtsu is l ...

Chiba Prefecture is a prefecture of Japan located in the Kantō region of Honshu. Chiba Prefecture has a population of 6,278,060 (1 June 2019) and has a geographic area of . Chiba Prefecture borders Ibaraki Prefecture to the north, Saitama Prefecture to the ...

and from Jogashima at the southern tip of the

Miura Peninsula is a peninsula located in Kanagawa, Japan. It lies south of Yokohama and Tokyo and divides Tokyo Bay, to the east, from Sagami Bay, to the west. Cities and towns on the Miura Peninsula include Yokosuka, Miura, Hayama, Zushi, and Kamakur ...

to the

Uraga Channel The is a waterway connecting Tokyo Bay to the Sagami Gulf. It is an important channel for ships headed from Tokyo, Yokohama, and Chiba to the Pacific Ocean and beyond. Geography The Uraga channel is at the southern end of Tokyo Bay (formerly ...

at the mouth of Tokyo Bay and extending to Natsushima in the city of

Yokosuka is a city in Kanagawa Prefecture, Japan. , the city has a population of 409,478, and a population density of . The total area is . Yokosuka is the 11th most populous city in the Greater Tokyo Area, and the 12th in the Kantō region. The city ...

Kanagawa Prefecture is a prefecture of Japan located in the Kantō region of Honshu. Kanagawa Prefecture is the second-most populous prefecture of Japan at 9,221,129 (1 April 2022) and third-densest at . Its geographic area of makes it fifth-smallest. Kana ...

. The Tokyo Bay Garrison Command was established in 1894. It was renamed the Tokyo Bay Fortress Command in 1895 and was headquartered at Yokosuka. Many of the 28-cm howitzers installed in the gun emplacements around Tokyo Bay Fortress were removed during the

Russo-Japanese War The Russo-Japanese War ( ja, 日露戦争, Nichiro sensō, Japanese-Russian War; russian: Ру́сско-япóнская войнá, Rússko-yapónskaya voyná) was fought between the Empire of Japan and the Russian Empire during 1904 and 1 ...

and were deployed to the

Siege of Port Arthur The siege of Port Arthur ( ja, 旅順攻囲戦, ''Ryojun Kōisen''; russian: link=no, Оборона Порт-Артура, ''Oborona Port-Artura'', August 1, 1904 – January 2, 1905) was the longest and most violent land battle of the Russ ...

, where they were deployed to devastating effect against the Russian Pacific Fleet. From the 1920s and 1930s, many surplus guns of the

Imperial Japanese Navy The Imperial Japanese Navy (IJN; Kyūjitai: Shinjitai: ' 'Navy of the Greater Japanese Empire', or ''Nippon Kaigun'', 'Japanese Navy') was the navy of the Empire of Japan from 1868 to 1945, when it was dissolved following Japan's surrender ...

, such as the 12-in

main battery A main battery is the primary weapon or group of weapons around which a warship is designed. As such, a main battery was historically a gun or group of guns, as in the broadsides of cannon on a ship of the line. Later, this came to be turreted ...

of the battleship which had been made available due to the reduction of capital warships per the London Naval Treaty and the

Washington Naval Treaty The Washington Naval Treaty, also known as the Five-Power Treaty, was a treaty signed during 1922 among the major Allies of World War I, which agreed to prevent an arms race by limiting naval construction. It was negotiated at the Washington Nav ...

, were reused in these coastal artillery installations. An important feature of the Tokyo Bay Fortress was a series of three artificial islands built between Cape Futtsu and Cape Kannonzaki at the entrance to Tokyo Bay in the 1910s. Equipped with 15-cm guns, this enabled the Tokyo Bay Fortress to cover the entire span of Tokyo Bay within firing ranges and provided a second line of defense against any ships which might have breached the gun emplacements at the entrance to Tokyo Bay. The third of these islands (the one closest to Cape Kannonzaki) was rendered unusable by

land subsidence Subsidence is a general term for downward vertical movement of the Earth's surface, which can be caused by both natural processes and human activities. Subsidence involves little or no horizontal movement, which distinguishes it from slope mov ...

caused by the

1923 Great Kantō earthquake The struck the Kantō Plain on the main Japanese island of Honshū at 11:58:44 JST (02:58:44 UTC) on Saturday, September 1, 1923. Varied accounts indicate the duration of the earthquake was between four and ten minutes. Extensive firestorms an ...

. It remnants posed an ongoing threat to navigation, and were removed from 2000 to 2007. All fortifications were dismantled at the end of World War II; however, the remains of the Sarushima Battery and Chiyogasaki Battery Yokosuka City official home page
were designated as National Historic Sites of Japan on March 10, 2015. This was the first instance of post-Meiji period military-facilities receiving this designation.

Components of the Tokyo Bay Fortress

Around Yokosuka

*Natsushima Battery *Sasayama Battery *Hakozaki Battery *Hashima Battery *Yonegahama Battery *Sarushima Battery (National Historic Site) *No.3 Kaiho

Miura Peninsula

*Jogashima Battery *Sendasaki Battery *Chiyogasaki Battery (National Historic Site) *Kannonzaki Battery *Misaki Battery *Tsurugizaki Battery *Kinugasa Ammunition Main Magazine *Oyabe Magazine

Boso Peninsula

* No.1 Kaiho * No.2 Kaiho *Futtsu Motosu Fort Battery *Kanaya Battery *Cape Taifusa Battery *Susaki 1st Battery *Suzaki 2nd Battery *Tateyama Navy Air Corps

References

External links

*{{Commons category-inline, Tokyo Bay Fortress History of Kanagawa Prefecture History of Chiba Prefecture History of Tokyo Coastal fortifications Imperial Japanese Army