There has been a shakeup in the Unites States Army. One female colonel has stepped down from her job after suggesting attractive women should not be portrayed in promotional materials. NBC's Kristen Welker reports.

A U.S. Army colonel who wrote an email suggesting attractive women should not be portrayed in U.S. Army promotional materials stepped down from her job Friday.

Col. Lynette Arnhart recently sent an email arguing that an attractive woman shown in a photo in an Army magazine sent the wrong signal. Arnhart argued that unattractive women are perceived as competent while attractive women are perceived as having used their looks to get ahead.

She went on to argue that the Army should use "more average looking women" or women who are willing to do the dirty work. Arnhart said that photos of attractive women in uniform lead people to ask if breaking a nail is considered hazardous duty.

Until she stepped down, Arnhart was in charge of the Army research project examining women's transition into combat roles.

"In order to protect the integrity of the ongoing work on gender integration in the Army, Col. Lynette Arnhart agreed to step down as the gender integration study director," an Army spokesperson said tonight.

The public affairs officer at the Army Training and Doctrine Command -- the recipient of Arnhart's email -- has also been suspended, pending the outcome of an investigation.

That officer, Col. Chris Kubik, sent NBC News a statement about the email earlier this week, saying that it "was an internal discussion; nothing more."

"This discussion was not and is not reflective of Army policy. The intent of the message was to help ensure that images depict professional female soldiers as they are, and to ensure they are recognized based on their hard-earned achievements as members of the profession of arms," Kubik wrote.