USS R-27 (SS-104) was an R-class coastal and harbor defense submarine built for the United States Navy during World War I.

The R-boats built by Lake Torpedo Boat Company (R-21 through R-27) are sometimes considered a separate class from those of the other builders.

[1] For surface running, the boats were powered by two 500-brake-horsepower (373 kW) diesel engines, each driving one propeller shaft.

Assigned duty with Submarine Division 1 in the Panama Canal Zone, R-27 got underway for her homeport of Coco Solo on 1 November.

Given hull classification symbol SS-104 in July 1920, she interrupted her five years in the Canal Zone with an overhaul at Portsmouth, New Hampshire, during the winter of 1921-1922 and a run to Pearl Harbor for exercises in early 1923.