Tenth Sontaran Battle Fleet

The Tenth Sontaran Battle Fleet was a Sontaran military unit commanded by General Staal and sent into Earth orbit in the early 21st century during the Sontaran invasion of Earth. The Sontarans planned to turn Earth into a cloning world. Command of the fleet took place from the flagship, which had many smaller support craft.

Luke Rattigan plotted with the Sontarans to assist them with the installation of ATMOS, designed to turn the atmosphere of Earth poisonous. The fleet waited, with the General in the flagship which had a teleport pod link to the Rattigan Academy near London, which Luke had created.

The flagship was destroyed by Rattigan after he sacrificed himself to end the invasion, as the fleet prepared to fire upon the planet. The explosion of the flagship destroyed the smaller craft around it. Because of the intervention of the Doctor, his companions and UNIT, the ATMOS plan had already failed. (DW: The Sontaran Stratagem / The Poison Sky) Though thrown off course by the blast, one Sontaran spacepod and its pilot, Commander Kaagh survived and crashlanding onto Earth. Alone on the planet, Kaagh attempted then to destroy Earth on his own. (SJA: The Last Sontaran)

Alternative timeline
In another timeline, the three members of Torchwood 3, namely Jack Harkness, Ianto Jones and Gwen Cooper, destroy the fleet. Ianto and Gwen die and the immortal Jack Harkness is teleported to the Sontaran home planet of Sontar. (DW: Turn Left)

Other possibly non-canonical information
Group Marshall Nathan and his subordinate, who had gained entry to the Doctor's TARDIS, also belonged to the Tenth Sontaran Battle Fleet. Nathan came from a time period sometime after 2001 (DW: A Fix with Sontarans).