I believe that units should not only be constructed with the right resources availble, but also if the correct city improvment is built. However this should only apply to some units, for example:
Missle Silo:
Nuclear Milssile
Cruise Missile
Air Base:
Fighter
Bomber
Helicopter
Missle Silo:
Nuclear Milssile
Cruise Missile
Air Base:
Fighter
Bomber
Helicopter
Comment