The third USS Alert was an iron-hulled screw steamer gunboat in the United States Navy. The lead ship in her class, Alert was destined for a long naval career, serving from 1875 to 1922, a period of 47 years, including service as a submarine tender in World War I. Toward the end of her career she received the designation AS-4. Alert was laid down in 1873 by John Roach & Sons at Chester, Pennsylvania in 1873. Launched on 18 September 1874, Alert was commissioned for the first time on 27 May 1875, Commander William T. Sampson in command.