The Horizon-class cruiser was a type of starship in Starfleet service during the late 22nd and early 23rd centuries. Similar in appearance to the Daedalus-class ships of the Earth Starfleet that were later integrated into the nascent United Federation of Planets Starfleet, the Horizon class was larger and more capable. (Star Trek: Avenger: "The Essential Process") It is unclear as to which Horizon — Daedalus-class or Horizon-class — was the ship that left the book Chicago Mobs of the Twenties on Sigma Iotia II. (TOS: "A Piece of the Action")