Siwash was built in 1916 by the Gas Engine and Power Company at Morris Heights, New York, as a private motorboat of the same name. The U.S. Navy acquired her from her owner, C. A. Schieren of New York City, on 18 June 1917 for World War I service. She was commissioned as USS Siwash (SP-12) on 18 August 1917.
Siwash patrolled in the 3rd Naval District in the New York City area until decommissioned on 10 May 1919. She was transferred to the United States Department of Commerce on 16 June 1919.