If you spotted low-flying military fighter jets today, the planes were likely involved in an interception and identification exercise around western Ohio, according to the North American Aerospace Defense Command.

The flights were scheduled between Cincinnati and Sandusky, NORAD reported.

“What we’re doing in this exercise is just practicing what is one of our most important missions in NORAD,” said spokesman Lt. Al Blodin based at NORAD in Colorado. “In the end, our job is to prevent another 9/11.”

NORAD, responsible for securing the air space of North America, practices exercises with a variety of scenarios, such as hijackings, planes flying in restricted zones or responding to unknown aircraft.

The aircraft involved in Wednesday’s exercise were a Cessna 182, a C-21 cargo and passenger jet, and F-16 fighter jets, he said.

NORAD has conducted the exercises since the start of Operation Noble Eagle after the Sept. 11, 2001 terrorist attacks.