From Halopedia, the Halo wiki
Silent Blade was a special operations unit of Jul 'Mdama's reformed Covenant.
During the Requiem Campaign, several members of Silent Blade were sent to eliminate UNSC forces in the area known as "the Refuge". After killing several Marines in Warbird Company they attempted to reach the safe room where Dr. Leslie Boyd was hiding. However, Spartan Fireteam Crimson was in the area and killed all the Covenant forces, including the Silent Blade assassins.