|USS Essex • USS Horizon|
According to the reference books Star Trek Concordance, Star Trek Encyclopedia (4th ed., vol. 1, p. 348), Star Trek Maps, and The Worlds of the Federation and the current startrek.com article, this vessel was the same starship Horizon that visited the planet Sigma Iotia II in 2168, as mentioned in TOS: "A Piece of the Action". In the episode, it was stated that the Horizon came "from the same outfit as" the USS Enterprise, but it was never specified if that "outfit" was Starfleet or the Federation, nor was the prefix USS ever stated. However, in a line taken from the captain's log found in the unrevised final draft of the script had described it specifically as the "Federation starship Horizon."
A reference model was eventually built by Greg Jein for Michael Okuda, who had it prominently featured in his works, firstly in his 1993 edition of the Star Trek Chronology, and subsequently in the first, 1994 edition of the Star Trek Encyclopedia, perpetuated as color photographs in all subsequent editions of both works.
A second display model was constructed by Jein to be later put in Sisko's office on a stand with a TNG-era communicator, where it can be seen in the background in numerous episodes, along with a model of the International Space Station, the Miranda-class USS Saratoga, and the Nebula-class USS Melbourne. 
It was also featured prominently in an article on the history of Federation starships, firstly in, and on the cover of, the Star Trek Fact Files (part 57, 1998) and subsequently in Fact Files' derivative publications Star Trek: The Magazine Volume 1, Issue 16 (pp. 6, 34, 2000) and Star Trek: The Magazine Volume 3, Issue 9, p. 32 (2003), in all cases featured as a CGI model.
For more information on the models, see Daedalus-class model.
In the first draft script of VOY: "Flashback", it was established that Harry Kim had never read the logs of the USS Horizon, though Kathryn Janeway recommended them to him. All mention of the vessel was excised from the episode by the time the final draft of the script was issued.
In the novel Starfleet: Year One, Captain Alonis Cobaryn (β) was mentioned as taking command of the Horizon in 2167. It was also mentioned in the Strange New Worlds VII short story "Test of Character."
According to the book Star Trek: Federation - The First 150 Years, the captain of the USS Horizon was Vince Waldron.