Yup, I can’t recall if it was a Rivet Joint or Cobra Ball (recce 707) that the Sovs thought it was.
The USAF was flying highly aggressive mission profiles, actively trying to get the Sovs to respond (but not to the point of a shootdown) this revealing their capabilities. Remember that this was the same time the USN was sending special missions subs deep into Sov territory to tap underwater comma cables.
Sorry, should be recce KC-135, not 707, in my above