USS Siwash (SP-12) was an armed motorboat that served in the United States Navy as a patrol vessel from 1917 to 1919.

Siwash in 1916-1917, prior to her U.S. Navy service
History
United States
Name	USS Siwash
Namesake	Previous name retained
Builder	Gas Engine and Power Company, Morris Heights, New York
Completed	1916
Acquired	18 June 1917
Commissioned	18 August 1917
Decommissioned	10 May 1919
Fate	Transferred to U.S. Department of Commerce 16 June 1919
Notes	Operated as private motorboat Siwash 1916-1917
General characteristics
Type	Patrol vessel
Tonnage	56 tons
Length	78 ft (24 m)
Beam	14 ft 9 in (4.50 m)
Draft	4 ft 1 in (1.24 m)
Speed	13 knots
Complement	15
Armament	1 × 1-pounder gun 1 × machine gun

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.