I had a course on it in NROTC but being far inland we didn't take sightings. Net result was that we could recognize a sextant and knew that one needed a really thick book of numbers to go with it - and an accurate clock.

Later, once aboard ship, the only contact with the sextant was to know where it was kept and maybe be invited to help inventory it once a year.

Navy Navsat was the predecessor to GPS and it worked faster and more easily than celestial nav - especially for a submarine.

GPS is near magical now. But can be turned off at any time. So old school skills could prove useful.
Still, taking sightings from a submerged submarine???? I hope not.