USS Gem (SP-41) was an armed yacht that served in the United States Navy as a patrol vessel from 1917 to 1919.

Gem was built in 1913 as a private steam-powered yacht of the same name by George Lawley & Son at Neponset, Massachusetts.

The US Navy acquired her under charter from her owner, William Ziegler Jr., on 26 March 1917 for World War I service.

Gem performed harbor entrance patrol at New Haven, Connecticut, until 12 December 1917.

In this duty, carried out at New York City; New London, Connecticut; Newport, Rhode Island; and New Haven, she experimented with camouflage defense, tested the Bates Automatic Course Indicator, and experimented with various submarine detection devices, including the Sanborn Speed Indicator.