There's three projects I've worked on that I've been particularly proud of. First was the Airfields Database. The year was 1989. I was just hired with a fresh BSCS degree, and working at what was then the Defense Communications Agency, in the basement of the Pentagon. My full TS/SCI clearance investigation was still ongoing, so I couldn't do any of that work. I only had an interim TS clearance. So that meant they had…
Circa 1984 (ish) I was in Australia and we didn't go looking for such wizardry .. it was easy enough to derive Great "Circle" paths about an oblate spheroid from first principals and, if required, weight the problem by wind strength, etc.
I was coding, at the time, for airbourne geophysical surveys at continent scale, so we were also pulling in IGRF models, normalising for diurnal magnetic flux, calibrating radiometric systems for air colum mass under craft | cosmic breakdown gammas from above, and all that jazz.
Was there anymore to your classified great circle code snippet than the correct geometric answer for a "not an actual sphere" .. or was the secret sauce just the exact series terms chosen and the order of computation in order to minimise error and reproduce consistent answers?
( I'm not asking for the revelation of the actual classified details, just curious about shape of the classified hole from the outside )