Knowland was reelected to the Fifty-ninth and to the four succeeding Congresses, serving from September 24, 1904 to March 3, 1915. His 3rd Congressional District included Alameda, Contra Costa and Solano counties. The U.S. Army's Benicia Arsenal and the U.S. Naval Shipyard at Mare Island were located in his district. Knowland had a keen interest in the military, most especially the U.S. Navy. He worked in Congress for capital ships to be built on the West Coast. He was an advocate for a two-ocean battleship fleet.