Sontaran scout ships, also called battlecruisers (TV: The Two Doctors) or battlespheres, (AUDIO: Starlight Robbery) were large, spherical spacecraft used by the Sontarans to scout in advance of a fleet to investigate or infiltrate the enemy.
When the Sontarans joined the Alliance, formed to imprison the Eleventh Doctor in the Pandorica and save the Universe, several Sontaran scout ships were part of the Alliance fleet which arrived at Stonehenge in 102 A.D. (TV: The Pandorica Opens)
In the 13th century, (TV: The Sontaran Experiment) Jingo Linx had to perform an emergency landing his ship, which was damaged on a reconnaissance mission, on Earth. Linx was forced to use his osmic projector to kidnap scientists from the future and equipment to repair his ship. Later Linx and the ship were later destroyed. (TV: The Time Warrior)
Several scout ships orbited the main Sontaran flagship during the Sontaran invasion of Earth in 2009. (TV: The Sontaran Stratagem / The Poison Sky) Kaagh was in one of these scout ship when it crashed to Earth. With his arm strap he moved the ship to a hidden location and even made it invisible. (TV: The Last Sontaran)