how do you make flavour units so that for example, usa will build super fortress (stats same as a bomber) instead of bombers?

1. Wrong Forum, questions belong to main creation & customization forum
2. by adding it as a new unit and assigning it to usa instead of the bomber

http://www.civfanatics.net/uploads3/Zulu_WRONG_FORUM_animation.gif

sorry, so if you assign it to usa like a unique unit will they build that instead of bombers, or do you have to disable bombers for usa?