Both of the above messages are correct. No sunglasses during BCT and your issued BCGs will not have transition lenses. It’s also important to know that sunglasses are not permitted to be worn while in formation. So unless a cadet had eye surgery recently, they can’t even wear them while marching for NMF so technically transition lenses aren’t allowed then either. HOWEVER, I know a few cadets who wear them anyway and since they are prescription lenses no one really gives them any problems.
Last piece of advice :: Squinting reduces the noticeable affects of smiling. Do with that what you will.