United States Army Grooming Standards

Each of the military services impose grooming standards on their military personnel, as part of their Dress & Appearance or Uniform regulations. For the United States Army, grooming standards are contained in Army Regulation 670-1:

".....Males will keep their face clean-shaven when in uniform or in civilian clothes on duty. Mustaches are permitted; if worn, males will keep mustaches neatly trimmed, tapered, and tidy. Mustaches will not present a chopped off or bushy appearance, and no portion of the mustache will cover the upper lip line or extend sideways beyond a vertical line drawn upward from the corners of the mouth. Handlebar mustaches, goatees, and beards are not authorized. If appropriate medical authority prescribes beard growth, the length required for medical treatment must be specified. For example, “The length of the beard will not exceed 1/4 inch.” Soldiers will keep the growth trimmed to the level specified by appropriate medical authority, but they are not authorized to shape the growth into goatees, or “Fu Manchu” or handlebar mustaches..."

Take that beards, goatees, Fu Manchu's and handlebars. Just goes to show that the mustache is the most dominant facial hair of all. If the U.S. Army supports the growth and maintenance of the MO, you should too.