On January 20, the Islamic State of Iraq and Syria launched its largest attack since their territorial defeat in Baghouz nearly three years earlier, on the Ghwaryan prison in Hasakah, Syria. In a surprise attack that appears well-planned, dozens of ISIS members on the outside launched a prison break to free their fellow militants. The prison had held a minimum of 3,000 people - including at least 700 minors - most of whom were brought there following the group’s defeat in Baghouz. At least 121 fighters of the U.S.-backed Syrian Democratic Forces (SDF) and prison guards and staff were killed in the assault, while an estimated 374 prisoners and attackers died during the 10-day long fight to regain control over the prison complex. Several thousand residents of Hasakah fled to other parts of the city to seek safety, while U.S. Special Forces assisted with Bradley fighting vehicles and airstrikes, in coordination with the SDF. The number of prisoners who escaped and remain at large is unknown, and threats of ISIS sleeper cells remain a constant threat in NE Syria, and daily raids and house-to-house searches have become the norm in an effort to root out the militants from the city.