USS Ensign (SP-1051) was a United States Navy patrol vessel in commission from 1917 to 1919.

In 1917, the U.S. Navy acquired her under a free lease from her owner for use as a section patrol boat during World War I.

Assigned to the 3rd Naval District, Ensign performed submarine net patrol duties in New York Harbor until May 1918, when was transferred to the 9th Naval District for service on the Great Lakes.

Arriving at Detroit, Michigan, on 14 June 1918, she patrolled until late in 1918, when the annual freezing over of the lakes brought the 1918 Great Lakes shipping season to an end.

[citation needed] The Navy returned Ensign to her owner on 30 January 1919.