This was one of many small monitoring stations that dot the Segmentum Obscurus, to watch for unusual activities, which may indicate the oncoming of a chaos attack. As it was a small station it was allowed low priority and only had a small contingent of Imperial Guard troops for defence accompanying a few tech-adepts to maintain the equipment. In 139M41, it was suddenly attacked and the compliment wiped out. Relief vessels found the crew massacred in a most brutal fashion. This was the first of a large series of small attacks by chaos spacemarines which heralded the onset of the Gothic Wars.
(Ref: Battle Fleet Gothic Rule Book)