USS Lillian II (SP-38) was an armed motorboat that served in the United States Navy as a patrol vessel in 1917.

Lillian II was built in 1909 by Willard Downes at Bayshore, New York, as a private motorboat of the same name.

The U.S. Navy acquired Lillian II from her owner, S. F. Rothschild of Bayshore, under a bare-boat charter on 6 June 1917 for World War I service.

She was enrolled in the Coast Defense Reserve on 8 June 1917, delivered to the Navy on 16 June 1917, and commissioned as USS Lillian II (SP-38) on 20 July 1917.

Assigned to the 3rd Naval District at New York City, Lillian II operated as a shore patrol boat in Great South Bay on the southern coast of Long Island, New York.