Thanks for that, however i still do not have any idea how these weapons stacked up against the best weapons in Europe at the time? or for how long they remained superior if that was the case before the Europeans came to posses similar weapons?
German infantry did not have repeating rifles in WWII. Does that answer the question?
BTW,



As for America "always" having a dominant airforce, they've only had a dominant airforce since the late, late Cold War. I'll be generous and say 25 years versus 230 years of independence and 400 years of English settlement in North America? Not a good choice IMO.
America wasn't a super power until after WWII, so the unit should probably be modern TBH (which sucks for them, but America shouldn't be a "civ" IMO, so too bad). Best UU candidate from the second half of the 20th century? I would have to go with nuclear supercarriers or an Abrams, so an upgrade on the carrier or modern armour (my vote would be for the carrier out of those two, as there are several tanks that are as good as an Abrams, but the US has the best carriers hands down).
If you wanted an earlier unit, I'd be hard pressed to think of one. I can't think of anything from the Revolutionary War period through to the Napoleonic era. I suppose cavalry is a decent choice from the mid-19th century (the existing model already looks like US cavalry, so they should keep that for the UU and the standard unit should be something different). However, I'd have to go with Ironclads from that period, since the US was really the only country to ever use them in combat. Super short lived unit though (maybe if you made it an early sub and other countries couldn't get it period, it would be useful?).
Other than that, I can't really think of anything that the US excelled at from the Civil War to WWII, beyond raw production. Maybe an earlier UU should really be something like India's fast worker?