Shark was built as the civilian motorboat Ildico IV in 1909 at South Yarmouth, Massachusetts. She later was renamed Shark. The U.S. Navy purchased Shark from her owner, Louis Herzog of New York City, on 17 May 1917 for World War I service as a patrol vessel. She was commissioned on 24 May 1917 as USS Shark (SP-534). Assigned to section patrol duty in the 1st Naval District in northern New England, Shark conducted harbor patrols there for the rest of World War I and for a few months after the end of the war.