Boeing has spent the last five decades repeatedly pitching all kind of different 747s to the US military, every five years or so.
Military cargo and civilian cargo, tanker, cruise-missile carrier, ballistic-missile carrier, fighter-carrier, airborne command post, President flying White House, and countless others.
Their one and only successes, have been the VC-25 and E-4, exactly SIX airframes.
Why on Earth would the US military buy A380s, even more at the time when the 747-8 barely survived it ?