For over a century, Mare Island hosted the Navy's Mare Island Naval Shipyard. The growing size and number of the country's naval fleet was making older facilities obsolete and led to increased building and refitting of shipyards nationally. In 1872, the U.S. Public Works Department commenced construction of a drydock on the island, setting it on a foundation of cut granite blocks. The work was completed in 1891. A second drydock was begun in 1899, a concrete structure long set on wooden piles; it was completed in 1910. By 1941 a third drydock had been completed and drydock number four was under construction. The ammunition depot and submarine repair base were modern, fireproof buildings. A million dollar, three-way vehicle causeway to Vallejo replaced a ferry service.