The Polaroid SX-70 was an SLR, perhaps even the world's first folding SLR, so
when Polaroid added sonar autofocusing to it, it became the first autofocusing SLR.
I don't have any film for mine, and the battery was in the film pack,
so I can't try it out, but my guess is that the focusing wasn't very good.
Not very targeted, anyway.
From a review of a later autofocusing Polaroid,
I understand that the sonar emitted a chirping sound.
Maybe an advantage if you were photographing birds?
Sonar wasn't really the way to do it—image analysis was,
which is how the Pentax ME-F
and Minolta Maxxum 7000 worked.
But
Sonar does have one advantage over visual focusing:
You can focus in the dark.
Here's an article from the July 1978 issue of Popular Science:
This ad is from the 30-April-1979 issue of New York Magazine:
This still is from an 11-minute informercial/instruction manual that tells the story of the SX-70,
including details on how it works and how to use it:
