"Bill Higdon" wrote ...
The F4-E's originally blown leading edge flaps (drooping leading edge),
in early to mid 1970's they were refitted with leading edge slats. Which
were controlled by a black box and interconnected so you didn't have one
out and one in, like the DC-10 that crashed in Chicago did.

The last F4 that I saw was at a local military airshow four or five years
ago. It had fixed leading edge slats bolted on to the outboard wing panels.
The pilot said it was a Wild Weasel airplane and one of the last F4s left in
the inventory. I'm sure it's been retired by now.

Rich