Firefighters from the 507th Civil Engineering Squadron participate in a 9/11 memorial stair climb, Sept. 8, 2019, at Tinker Air Force Base, Oklahoma. This year marks the 12th anniversary of the CES fire climb, during which the Reservists climb up and down a three-story fire training tower 14 times to honor the 343 firefighters who perished during the attacks on the World Trade Center, Sept. 11, 2001.