On 3 May 1898, Uncas, in company with revenue cutter USS Hudson, captured off Havana the Cuba-bound Spanish sailing vessel Antonio Suarez.

In the autumn of 1899, Uncas inspected lighthouse facilities in the Danish West Indies and at Puerto Rico before she served a brief tour towing United States Army Quartermaster Corps barges.

She then resumed lighthouse inspection and harbor survey duties in the Puerto Rican area and, during this tour, carried a selection board to Culebra Island to seek out a site for a target range.

Sandwiched in between her routine operations, she towed the disabled merchant ship SS Longfellow from Arecibo, Puerto Rico, to San Juan for repairs on 14 November 1901.

When the Navy adopted an alphanumeric hull number system for classifying its ships in mid-1920, Uncas was redesignated as fleet tug AT-51 on 17 July 1920.