Enlisting is a very viable option for you
If you know for sure you want to go to the Academy, enlisting is a very viable option. Given your poor academic performance in high school, your application to be a mid is going to be a long shot, so your absolute first requirement would be to get a record of straight A's at your local junior college. With your D's as a sophomore, it will be very difficult ( but not impossible ) to get into USNA. If you have a full year of JC transcripts of straight A's ( or something close to it ) that, combined with enlisted service in the NAvy or Marine Corps, might be enough to get you in.
I went straight into the Marines out of high school. I had mediocre high school grades (3.0) but due to very high SAT / ACT scores, and exceptional military performance, I was offered a direct admission route to the Academy.
If you can string together three - four terms at your junior college of straight A's in relevant courses - math, chemistry, physics, english, history - enlisting would be a very viable option for you.
Consider your timeline - you have to be AT the academy before you turn 22 - so you can't afford to spend more than a year at a JC getting your academic grades up to speed. If you graduated in June of 2006, and spend a full year in JC getting straight A's, then enlist, you would be very competitive for direct admission to the Academy, as long as you have enough time to spend 18 months "in the fleet" as a Sailor, to build a track record of enlisted evaluations to support your desire to be accepted to USNA.
