During her second deployment to Iraq, Staff Sgt. Stacy Pearsall of the Air Force found herself attached to an Army ground unit that was clearing roadside bombs. They had just found their 26th device of the day when one of their armored personnel carriers exploded. An ambush was on.

The chaos that unfolded over the next few hours was not a typical day for Sergeant Pearsall. But under the Pentagon’s decision to allow women into front-line combat units, officially announced Thursday, it could become much closer to the norm for women in American uniforms.