Mare Island Naval Shipyard - Wikipedia The Mare Island Naval Shipyard (MINSY) was the first United States Navy base established on the Pacific Ocean. It is located 25 miles (40 km) northeast of San Francisco in Vallejo, California.The Napa River goes through the Mare Island Strait and separates the peninsula shipyard (Mare Island, California) from the main portion of the city of Vallejo.. MINSY made a …