I lived just to the north within Yokohama city limits and worked in Yokosuka (not on the base). The JR Yokosuka station dumps you off in the middle of nowhere. If you want to go to Yokosuka, take the Keikyu line, and keep going south to the end of the line, then take the bus to the sea side park, or get off at Kurihama and take a look at the fist place Com. Perry landed on the quest to open Japan for trade. The main part of Yokosuka is dominated by the nearby US Navy base, and is kind of sleazy.