Validation, post-grad and other paths
usnajosh, accenting the positive here, college courses can aid in validation of courses at USNA, though not carrying over the credits, by moving a mid ahead of their peers on his/her academic matrix. That may position the mid to take advantage of Master's programs.
The Master's program mentioned above, where all undergrad work is completed end of senior year first semester, and second semester is spent commuting to nearby grad schools, is VGEP. Those degrees are normally completed by Dec of the class year of graduation.
IGEP is when the recent grad heads directly to the Master's program after graduation and not to the Fleet or Corps for warfare training and assignment.
Here's a good sample link below for the Computer Science Dept. Looking at the similar departmental pages on the usna.edu site will show which departments have VGEP and IGEP opportunities and how many. Click on VGEP and IGEP to get details.
http://www.usna.edu/CS/academics/vgep.htm
Here's the Mech E Course page with link to each course. You can compare what you're taking now to what's offered. If you land in 2015, the coursework you're doing and how well you're doing, will play into the validation process.
http://www.usna.edu/MechEngDept/courses.php
Googling "naval academy engineering department" will send you to a number of links for various engineering majors.
Of course, this is all w-a-a-a-y down the road for you, but best of luck in landing a spot in 2015. If you really want to be a Navy or Marine Corps officer, and USNA or ROTC are not in the cards for you, don't rule out OCS (or Marine Corps equivalent post-college commissioning programs) if you continue and get your B.S. in Mech E. The Navy always needs good engineers. See this link, which describes the process for gaining a commission and then going on to being a nuclear submarine officer.
!!!Please note, under Educational Opportunities, the Nuclear Power Officer Candidate program, a generous scholarship and bonus program designed specifically for undergrads who know they want to go Navy in this field - but are not at USNA or NROTC.
http://www.navy.com/navy/careers/nuclear-energy/submarine-warfare-nuclear.html