Captain Carol Freeman and her elite team
Commander Jack Ransom commanding a special ops team
Captain Morgan Bateson and his elite team
Starfleet special forces or Starfleet black ops was any secret or elite team or unit that performed special operations on behalf of Starfleet and the Federation. Members of such teams often wore black uniforms and or tactical vests, some of the more elite were given nicknames, such as "The Cleaner" or "The Ghost".
During the Klingon War, Starfleet special forces were involved in many front line battles and were tasked with the assassination of opposing military leaders. (SNW: "The Broken Circle", "Under the Cloak of War")
Many black ops agents were secretly stationed aboard Federation starships during the Dominion War. (LD: "Mugato, Gumato")
Upon her transfer to the USS Cerritos, Ensign Beckett Mariner started a rumor that she was a black ops secret agent trained to be the "perfect weapon", who was somehow responsible for the mysterious catastrophe that befell her previous post, the starship Atlantis. Honus, a bartender on the Cerritos, repeated this rumor to Ensigns Brad Boimler and Sam Rutherford in 2381. (LD: "Mugato, Gumato")