Good questions that do come up. For the most part your major has little to do with what you do in service. If you major in Aero will it help with flying? If you are a Nuke Engineer who will find nuke school easier? Possibly to understand some concepts, but actually flying a plane, handling a sub, leading people, probably not much. Cyber might be the one major and then career choice that does relate. Where I do think your degree matters are what are considered shore tours or B billets (Marine lingo). If you want to earn a grad degree in engineering then go work helping the Navy to design, test and field the next generation of ship, plane, radar system, weapon, ejection seat, etc. then a degree like Engineering will help to get there. Will you remember everything from undergrad no? Will you be fine, yes. Remember USNA’s goal is to create unrestricted line officers who will hit the fleet to do their jobs and lead people. Regardless of job, you will lead people. Even a new pilot will have some job outside the cockpit managing people and something else in the squadron.
I was a history major at USNA. I spent my time doing typical Marine things (leading, training, crayon eating, etc) while at home and deployed. It’s really the problem solving, innovation, critical thinking, analysis, writing skills, speaking skills that I learned and refined at USNA that I used daily as a Marine. Most my friends say this too. After I got out I started as an Analyst then moved quickly to being an engineer and manager. It was those same skills that I learned at USNA that had me move up quickly gaining responsibility, more decision making, managing more people, etc. Even as a history major I was working side by side with engineers from GT, Auburn, Fl St, MIT among many others. Pretty quickly they all worked for me. I now hold multiple masters and never had an issue with any grad program.