Think it was in use up into the mid 60’s. Just tacking a couple fans on the wings does not make it in the jet age!. An interesting stopgap measure.

TAC used the KB-50 as three point hose & drogue tankers until the mid 60s.
There are all kinds of photos showing them with F-100s, 101s, 105s, B-66s.
I have read one account of them being used over Vietnam. If it happened, it happened early in the war. As a kid, I recall seeing a lineup at Johnson AB, Japan in 1963.

Interesting note. The KC-97s of course, had the same wings, and when the “L” models were converted, they used the entire outer wing panels from mothballed KB-50s.

The KC-97L came about after a pilot with the Illinois ANG out of O’Hare suggested the jet agmentation as a safety measure to help get the loaded aircraft off from “short” (i.e. not SAC 13,000 ft) runways. The extra cruising speed didn’t hurt either.
Of the few surviving K/WB-50s, at one time the Pima museum had two.
The other aircraft is now at Castle.
I visited Pima within days of their opening in 1976 and beyond a rope “Do Not Enter” area (which of course I entere…after all there was a wingless F-94 lying there!) there was a B-50 fin laying on its side in the sand, its fabric rudder in tatters.