I guess you saw post 76, Rickover hand picked him.
Read my post 83 again CAREFULLY. There is a very huge difference in a land base design team and being a crew-member. Even being selected for a crew-member status still doesn't guarantee it. Subs and ships undergo very strict operational readiness evaluations {Sea Trials} at sea under simulated combat and disaster/casualties situations and Officers must give correct responses. Rickover would likely not head up that team BTW. Those teams can end commissioned careers or get Nuke Officers placed elsewhere such as Deck Dept Officer on a conventional ship instead. The same for enlisted as well when it comes to the Nuke Program and even more so to the submarine fleet. One mental lapse especially by an officer can end ones time as a Bubblehead.
The MPA I had his next duty was heading a propulsion plant examination team on a readiness evaluation team.
Further to the point some engineers can function on a genius level in a textbook or planning environment but lack the ability and judgement skills needed to become operational engineers. IOW book smart and that’s it. Carter would not have been taken to the sub and Rickover say here ya go Jimmy.