The USAF started doing away with the Sextant and Cel Nav in the KC-135 in the late 1990's - early 2000's with the PACER CRAG mod (CRAG=Compass, Radar And GPS). This also eliminated the Nav position, however the ANG and Reserve kept many older navs on to allow them to retire. Younger Navs had the opportunity to cross train, some going to flight school to become pilots. I'd say we haven't used the Sextant in about 5-6 years.

For the C-130 inthe USMC, I believe they taught shooting cell until around 2002 or so. using the Sextant was basically not needed due to dual INS, GPS. The school house still taught it and we did training flights with the student nav's in the back of the herk plotting and all. I do know it was early 2000 for that when it stopped.