Some of the kit I worked on in the military had crypto loads downloaded to them (Radar warning receivers, comms kit, etc). If we had to destroy them, it was mallet the hell out of them with lump hammers, put them in a pile and get the welders to give them a good going over with an acetylene torch. Same with floppy disks (it was a while ago), anything with anything above restricted got properly torched. No way anyone was getting anything off them.
A really weird thing though. We had some paper documents that were on a plastic material. Whenever we did updates we would have to burn the sheets. These things would sort of shrivel up up were readable for a while until the plastic finally gave up the ghost.
