In the Army (I presume this applies to all Armed Forces) hairpieces are not allowed unless to cover natural baldness or physical disfiguration. When worn, the hairpiece must essentially conform to the standards of a normal haircut meaning that the hairpiece cannot interfere with the wearing of hairpieces (especially a kevlar, also a gas mask). I know a couple of guys that I was deployed with a couple of years ago that had hairpieces, but decided to ditch them for deployment. One just walked around with a close MPB buzzcut the other just shaved it all off.