hi,

NDA recruitment is conducts for admission to Army, Navy and Air Force wings of NDA and Indian Naval Academy Course (INAC), however you can do b.tech , since choice is given to naval and air force candidates after completing their training program, but you need to serve in navy or in airforce,

however if you are really enthusiastic for naval or marine engineering, you can go for marine engineering course in reputed organization and can become a naval architect.