No, it was no secret use
It was when I was working for EXLOG (a mud logging company) on the oil rigs.
The Geologists would load the programs from 8" floppy discs. If I remember rightly, all it was used for was working out the bore hole dimensions and characteristics. It was a glorified calculator.
The 8" floppies were in a 19" rack configuration and in a bank of 4. For some reason they were always on the top slot of the 19" rack and weighed around 35 kgs. I very often had to change these single handed trying to juggle them into the optima slide rails. Considering I only weigh 70 kgs myself, it was a real challenge.