The Skirmish on Brennus was a short battle waged several years into the Human-Covenant War. It was also the first time that the SPARTAN-II Sigma Team came into contact with Covenant forces after several years of being deployed exclusively against Insurrectionist foes.
The Spartans were deployed to investigate a research station on Brennus, a sparsely populated planet in the Outer Colonies. Upon their arrival, the team found that the station had been taken over by Covenant forces, who had killed everyone inside. Knowing that they were outnumbered by the enemy, Fenn-145 ordered the team to split into threes, spreading out in the area surrounding the facility. Upon doing this, the Spartans opened fire from multiple directions, giving off the impression that they were a larger force than they actually were.
With the Covenant defenders pushed back by Sigma's relentless assault, Marco-035, Wulf-041 and Nef-015 were able to make their way into the station's perimeter, killing a number of Sangheili who were attempting to extract information from the databanks there. As they moved through the occupied building, the three Spartans came across an unknown type of Covenant species. As it appeared to be taking information from the research facility, Nef-015 killed the creature to prevent any navigation data from being stolen. The remaining Covenant soldiers were swiftly mopped up by Sigma Team within an hour, leaving no survivors.
This engagement marked one of the first known sightings of Covenant Engineers on the battlefield. Nonetheless, the Cole Protocol was carried out effectively and the attempted Covenant occupation was successfully thwarted by Sigma during this skirmish.