USS S-19 (SS-124) was a first-group S-class submarine of the United States Navy. She was in commission from 1921 to 1922 and from 1923 to 1934 and served in both the Atlantic and Pacific Oceans.

The United States' S-class submarines, often simply called S-boats, were the first class of submarines with a significant number built to United States Navy designs. They made up the bulk of the USN submarine service in the interwar years and could be found in every theater of operations. While not considered fleet submarines, they were the first submarines in the USN designed for open ocean, blue water operations. All previous submarines had been intended for harbor or coastal defense. These boats were intended to have greater speed and range than previous classes, with improved habitability and greater armament.