The Spacefleet was a human-based organisation which existed from the early 26th century until (and most likely after) the Earth Empire's fall in the 30th century. (PROSE: Love and War, Original Sin) It was affiliated with both the Earth Empire and the Earth Alliance. (PROSE: Return of the Living Dad)
The Spacefleet operated a number of facilities, including boarding schools for children of members of the Spacefleet. One such school was operated on Mal Oreille. (PROSE: Biology Lesson on Mal Oreille)
In 2547, Admiral Isaac Summerfield and a fleet of ships encountered a Dalek fleet and fought at Bellatrix. In destroying the Daleks, the Admiral's ship, the Tisiphone, fell into a spatio-temporal rift, taking it back to Earth in 1963. (PROSE: Return of the Living Dad)
Following her father's disappearance (and apparent death) and her escape from foster families, Bernice Summerfield was enrolled in the Spacefleet military academy. She showed an aptitude for the life of a soldier within the Spacefleet, and might have made Section Leader, had it not been for her disciplinary record. (PROSE: Love and War, The Tunnels to Heaven) She escaped from the Spacefleet by bailing out of a troop ship in an escape pod on the way to Capella.
Ace joined the Spacefleet for three years after the battle with the Hoothi on the planet Heaven, becoming an explosives expert. She encountered a Spacefleet-created clone of Abslom Daak. (PROSE: Love and War, Deceit)