In 1063, Muraoka Tamemichi established Kinugasa Castle in what is now Yokosuka. He took the surname Miura. The castle fell during the Battle of Kinugasa in 1187. Miura Oosuke Yoshiaki died at that time.
In 1253, Nichiren began teaching in the region.
The adventurer William Adams (inspiration for a character in the novel Shogun), the first Briton to set foot in Japan, arrived at Uraga aboard the Liefde in 1600. In 1612, he was granted the title of samurai and a fief in Hemi within the boundaries of present-day Yokosuka, due to his services to the Shogun. There he founded a family with Oyuki, the daughter of Magome Kageyu, a noble samurai and official of Edo Castle. William and Oyuki had a son called Joseph, and a daughter, Susanna. A monument to William Adams (called Miura Anjin in Japanese) is still visible in Yokosuka.
In 1853, United States naval officer Matthew Perry arrived in Tokyo Bay with his fleet of Black Ships and came ashore near present day Yokosuka, leading to the opening of diplomatic and trade relations between Japan and the United States.
Yokosuka became the first modern arsenal to be created in Japan. The construction of the arsenal was the central point of a global modern infrastructure, that was to prove an important first step for the modernization of Japan's industry. Modern buildings, the Hashirimizu waterway, foundries, brick factories, and technical schools to train Japanese technicians were established.
Yokosuka was to become one of the main arsenals of the Imperial Japanese Navy into the 20th century, in which were built battleships such as Yamashiro, and aircraft carriers such as Hiryū and Shōkaku. Major naval aircraft were also designed at the Yokosuka Naval Air Technical Arsenal.
Between 1938 and 1945 more than 260 caves in more than 20 separate tunnel/cave networks were built throughout the base. There are 27 kilometers of known tunnels on the base. Many more tunnels are scattered throughout Yokosuka and the surrounding areas. During the war, these tunnels and caves provided areas in which work could be done in secrecy, safe from air attacks. A 500 bed hospital, a large electrical power generating facility, and a midget submarine factory and warehouse were among the many facilities in caves around the base. During the war, more than 800 personnel actually lived in these caves. Each naval base department was ordered to dig its own caves, which accounts for the lack of an overall organization to the cave and tunnel system. In 1992, a complete survey of all known caves was conducted, and all the caves except for three still in use were sealed up for safety reasons. The cave that is currently used as a command bunker by the US military was used for several years after the war to grow mushrooms, which were sold in the commissary for three yen per box.
The base has been used by the US Navy since 1945, and is the largest naval facility in Japan.
The battleship Mikasa, flagship of Admiral Togo at the Battle of Tsushima, built in Britain by Vickers, is preserved on dry land at Yokosuka. It is a museum, complete with actors dressed like members of the original crew, and can be visited for an entrance fee of 500 yen.
As of 2007, the city has an estimated population of 423,576 and a density of 4,286.74 people per km². It covers an area of 100.62 km². It is the 11th most populous city in Greater Tokyo, 12th in the Kantō region.
Yokosuka now is home to one of the biggest military seaports shared by the United States Navy and the Maritime Self-Defense Force of Japan. The US Navy nuclear powered USS George Washington is currently "forward deployed" and en route to it's home port at Yokosuka Naval Base. On October 28, 2005, the US Navy announced that in 2008 the USS Kitty Hawk will be replaced by the USS George Washington'', a nuclear powered Nimitz class carrier. A US Navy spokesman said the decision was a mutual agreement between the United States and Japan. Hiroyuki Hosoda, a top spokesman for Japan's government, said, "We believe that the change (of the carriers) will lead to maintaining the solid presence of the U.S. Navy and contribute to keeping Japan's security and international peace into the future." This would be the first time a U.S. nuclear powered ship would be permanently based in Japan. In an attempt to explain the carrier's mission to the Japanese public, the U.S. Navy has printed a manga about life aboard USS George Washington, titled "CVN-73".
The Club Alliance enlisted club, which lies just inside the main gate of Yokosuka Naval Base, opened in 1983. It replaced the old Club Alliance which was demolished to make way for the Prince Hotel. The old Club Alliance is where Ryudo Uzaki got his start playing rock and roll.
The Honch, a mecca for shopping and nightlife and located just outside the Yokosuka Naval Base's main gates, is a popular attraction for tourists and sailors stationed nearby, as well as local Japanese residents.
Many Nissan and Infiniti automobiles, such as the Nissan Maxima and Infiniti G20, were assembled in the 520,000 square metre Oppama plant (追浜工場) in Yokosuka. The plant has been said to have played a significant role in Nissan’s revival with its one car per minute output and quick four day reconfiguration between assembly of various autos. The plant is adjacent to Nissan's Research and Development Center, the Oppama Proving Ground and the Oppama Wharf, from which Nissan ships vehicles made at Oppama and Nissan’s other two Japanese vehicle assembly plants to other regions of Japan and overseas to other global markets.
The city operates one municipal high school, Yokosuka Sogo High School.