Optics in use by US Military

[msp21]

I recently read an article which stated the Marine Corps was going to phase out legacy M16 iron sights.
Does any branch of the military still use iron sights as their primary method of sight acquisition?
More specifically, do any infantry units still use iron sights or has everyone transitioned to optics?

[turnburglar]

When I was deployed in 2013, everyone that had even some sembalance of a 'hitter' had full daylight/night capabilities on their carbines. The only people walking around with ironsights where like maintainers, comm folk, intel, chow hall.... i.e. if bad guys show up, call the pros.

[Iraqgunz]

This subject has been covered NUMEROUS times.