At the time the F4 was selected as the interceptor/ground attack
aircraft for all 3 services, I was an engineer with the Air Force
Systems Command at Wright-Patterson AFB. Later, I was on the evaluation
team that selected the navigation/bombing system for the F4C. MacNamera
was Secretary of Defense at the time an wanted the services to use a
common aircraft to reduce the cost of maintenance and training. Also,
this would reduce the development costs for navigation, missiles and
other equipment designed to work with the plane.
I doubt very much there was significant planning for the F4 to be used
in Vietnam. The rapid build-up in Vietnam seemed to take most of the
military by surprise. You can get a better aspect of this from
MacNamera's book: Blundering into Disaster. For a broader perspective,
see Barbara Tuchman's, In Pursuit of Folly.
Richard Waddell