It was Friday the 13th of May, and an ominous figure was lumbering forward through an office building here. The sound of erratic gunshots echoed down the hallways. “Exercise, exercise, exercise!” yelled an unspecified voice trailing the aggressor. The clarification didn’t lower the volume of the mock gunfire.

The red-vested pretend assailant kept advancing, firing blank rounds within the confines of the office structure. Through the din, the trailing voice reassuringly repeated, “Exercise, exercise, exercise!”

Guardsmen of the 111th Attack Wing and first responders from Horsham Township, Pennsylvania, were participating in a major accident response exercise involving an active shooter and mass causalities.

But unlike some military installations, when the 111th ATKW conducts a MARE, the exercise isn’t isolated to base personnel. In fact, local agencies such as Pennsylvania’s Montgomery County’s  SWAT team, Horsham Township Police and Fire Departments play as important a role as the military units.