38 USC 2410 - Burial of cremated remains in Arlington National Cemetery

(a) The Secretary of the Army shall designate an area of appropriate size within Arlington National Cemetery for the unmarked interment, in accordance with such regulations as the Secretary may prescribe, of the ashes of persons eligible for interment in Arlington National Cemetery whose remains were cremated. Such area shall be an area not suitable for the burial of casketed remains.
(b) The Secretary of each military department shall make available appropriate forms on which those members of the Armed Forces who so desire may indicate their desire to be buried within the area to be designated under subsection (a).