I've used one of these for years in a SCIF. http://www.whitakerbrothers.com/datastroyer-101-cd-high-security-shredder
I have some Global knives and they aren't cheap. I would have used a more appropriate tool.
I was at "Schriever" (Falcon back then) from 1992 to 1994 and the GPS DASDs were being replaced. I know, as I was in the GPS module on a daily basis and the new drive enclosures were microscopic compared to the DASDs. Not sure where the GPS DASD references are coming from. The GPS module was the first to replace the DASDs as they had all the money. San