SASless, be fair. GPS was not available for civilian used until the mid eighties. The Nigerians may have used it but there was no guarantee that it would be available when you needed it. It wasn't until the turn of the century that Selective Availability was turned off and one could fix their position within the rotor disc. As an example; before then, Chinese airliners were tracking their airways with ADF and DME because they believed that the Americans could turn off the satellites in their area without warning. I had a GPS in my aircraft and their pilots would stare at it open-mouthed.
IIRC before LORAN, DECCA was the primary area navaid in Viet Nam so it must have been some use.