I’m a rising high school junior taking dual-enrollment and college classes, what is the process like for me to not need to retake the classes because I’ve already earned the credit?
Credits from outside institutions do not 'transfer' to service academies. There is a process by which you may be able to validate classes (this typically happens during the plebe/cadet summer).
If you have AP test scores, those may also be taken into consideration. Validating may make a more difficult major more doable, or free up time for a minor, or if an all-star scholar, a dual major. Nobody graduates a semester early like civilian colleges sometimes offer.