Flight Instructor with student reported a formation of military helicopters in the traffic pattern turned into their flight path resulting in the Flight Instructor taking evasive action to avoid a collision.

Narrative

Traffic pattern event involving training aircraft and military helicopter formation. I was downwind to base for RWY XX R at about 500ft to 400ft. A military formation flight had just taken off from the ramp and was instructed to fly between the parallels as we have that for normal operations. My student was PF initially as they were in the process of training the traffic pattern; the formation helicopters initially were correctly flying the parallels flying west; then suddenly made a left turn to the south-southwest directly into our path; wher upon that observation I took controls; and the helicopters continued to fly right under our aircraft at about a difference of less than 100ft (approximation because our altitude was 600ft trending down and they were instructed to fly the parallels at 500ft; as per procedure). Considerations in that moment were more evasive than reprimanding as my only focus was maintaining separation. The lead helicopter was instructed to make a phone call to the tower. Thankfully nothing actually happened.