I think the above poster is saying that it is almost impossible to go into "support" fields in the USN out of USNA. These would include intel, supply, aviation maintenance, logistics, medical service corps, engineering duty, etc. The USN allows those only if you're NPQ for line. So, 95% of grads will drive ships or subs, be an aviator or SEAL or go USMC -- with a very small number in each class going to med school, cyber, etc.
The USMC I believe offers "support" roles based on preference, how you do at TBS, needs of the USMC, etc.
I also believe (someone please correct me if I'm wrong), that grads from USMA and USAFA can directly commission into "support" roles even if qualified for "direct combat" roles such as pilot, infantry, artillery (note: I'm using the quoted terms colloquially). In fact, I believe that a decent portion of each class must go into those fields. However, you'd have to go to the USMA/USAFA forums to see how the process works (i.e., how likely you will get a support billet and how much choice/say you have in the process).
This is why BGOs (should) preach to candidates that they are almost certain to go into an URL community, including the USMC. And that, if their heart is set on being a supply officer or aircraft maintainer, it's unlikely to happen out of USNA, except possibly through the USMC for certain fields.
That said, if you do want a combat specialty, USNA offers the greatest choice. At USAFA, it's pilot or something else. At USCGA, it's mostly sea-based. The USA doesn't offer much in the way of aviation to non-warrants and doesn't drive ships. So, if you know you want line but aren't sure whether you want ships, subs, aviation, spec war, or ground, USNA offers the "most" choices.
As an aside, a Group 3 major could go subs or nuke surface. He/she must have done really well in the technical courses and also must be screened. It definitely happens, but isn't common.