The USS Sherlock Holmes (NCC-221B) was a Federation starship that was in service with Starfleet in the mid-24th century. In 2364, the commanding officer was Captain Jeffery Joal Annon.
In 2364, prior to stardate 41603.7, this ship, along with the USS Unicorn, received an order from Admiral Gregory Quinn of Starfleet Operational Support Services.
At the end of that year, Data read these orders and several others to investigate claims of a conspiracy among the highest members of Starfleet Command. (TNG: "Conspiracy")
The ship was never mentioned in dialog; this name came from a mission order.
The ship might have been named after the famed fictional detective
, Sherlock Holmes
. The registry was an in-joke
as it was the house number of Holmes' residence on Baker Street, 221B.