A Terran Dominion science team was sent to Taurus IV in order to investigate potential protoss relics on the surface. However, the Dominion lost contact with them. The 21st Assault Division was sent to investigate.
The 21st, under a new recruit, set up a mining base and a small force of marines. However they seen discovered the planet to have a zerg infestation. The division pushed through a line of zerglings, and discovered the science team had been all killed by the zerg.
Blizzard Entertainment. StarCraft II. (Activision Blizzard). PC. Mission: Field Duty (in English). 2016-06-20.