Norden bomb sights used human hair for at least part of the crosshairs that were a part of the (as I understand it, rather complex) reticle. I read a fascinating interview with an old woman who, as a young girl, was screened for the quality of her long hair as a part of the war effort. Neither she nor her parents understood but went along with it. When the government came back and asked her to donate her hair, there was no hesitation. After a wash and comb, she let her hair get chopped off right at the scalp. She didn't find out how her hair was used until well after the war.