🚀 go-pugleaf

Aargh!  There is not just one definite regulation covering this.
AR380-380 is the Army's main Regulation covering computer security,
but there are other documents too, some classified and some not.
Generally disk packs, magtapes, MOS memory, etc. used for routine
SECRET data storage can be overwritten a sufficient number of times
with alternating patterns; otherwise the media can be "degaussed",
although it may mean sending your media via authorized courier to
some place with appropriate facilities.  Some categories of
information (e.g. SI) are considered too sensitive to take any
avoidable risk, and for them the pattern overwriting method is
unlikely to be authorized.

The only safe thing to do is to consult your local ADP security
office.  If they don't know the regs, it's their job to find out.