Gravel mines
（重定向自Gravel mine）
Gravel mines, also called Button mines, were small U.S. made air-dropped anti-personnel mines. They were used extensively during the Vietnam War as part of the McNamara Line. They were also used as a rapid-deployment area denial expedient, to provide a barrier during combat search and rescue (CSAR) operations between downed pilots or other endangered units and infantry threats.