NavList:

gl wrote: Here is the photo of the Kollsman periscopic sextant mount in one version of the Boeing 707. This particular airplane carried President Reagan all around the world. I wouldn't be at all surprised if the current presidental planes had these mounts. Can't be jammed like GPS and passive, no electronic emissions to attract attention.

A presidential jet flying at the tropopause with a spare crew member might be one of the few places that 1970s style celestial would be worth pursuing as a loss of GNSS solution, because celestial would be available almost all the time.  However it would be a brave crew that descended towards high ground trusting only to a celestial fix.  It would get you to the correct country though.  There being no charge inside a hollow conductor, an existing sextant mount would have been a useful place to stick up an aerial for an early GPS set as was done in the RAF Dominies.  Moreover, it would be a great place to stick up the Stars and Stripes after landing. DaveP