Stealth vs. Mobile Stealth Bomber Wing

Can anyone explain what the difference between these two items are?

The only difference I noted was Mobile Stealth Bomber Wing consisted of 4 more bombers than a regular Air Force Stealth Bomber Wing.

Is there something else that sets this apart? What does the "Mobile" part actually do for it?

Mobile units require professional soldiers and officers, that you can purphase with with Gold coins via Direct Trading

Mobile units can be loaded into a space center, and transported via space shuttles. To another country on the same world, or a country on another world. Or to and from a space station that you can buy and sell whole units from

additionally, mobile units can be upgraded higher than other units.