RPMs were originally developed for screening individuals and vehicles at secure facilities such as weapons laboratories. They were deployed at scrap metal facilities to detect radiation sources mixed among scrap that could contaminate a facility and result in a costly clean up.  As part of the effort to thwart nuclear smuggling after the breakup of the Soviet Union, RPMs were deployed around that territory, and later around many other European and Asian countries,  by the US Department of Energy (DOE) National Nuclear Security Administration (NNSA) Second Line of Defense Program (SLD) starting in the late 1990s. After the attack of 9/11, the US Customs and Border Protection (CBP) started the Radiation Portal Monitor Program (RPMP) to deploy RPMs around all US borders (land, sea and air).