Advice for a veteran getting accepted into a great university for engineering?

I had a 3.0 GPA in HS (I know its not good). I was having issues early on but the last 2 years i did amazing, even throughout HS I was always enrolled in AP/Honors classes. I took the ACT my last year of HS and scored a 25. Well I’ve been in the military for 2 years now (going to schools) and am gonna start an online class soon. My question is when I get separate from the Military what can I do, If anything, to increase my chance of getting accepted to a great university for engineering? I’m only gonna take 1 or 2 classes at a time while I’m active duty so maintaining a high GPA wont be as difficult as being a full time student. If I maintained a high GPA while active duty and worked on my ACT to about 30-32, would I have a good chance of admittance to a great university for engineering even though i have a poor HS GPA? I know all of this will not be easy but I know I can do it. I’ve grown tremendously as a person since joining the military and want this bad, but I feel my mistakes of the past are going to hold me back. Also will online classes look “bad”? I want to take classroom courses but my ship can leave at anytime so if anything happened I’d have to drop the course. First time on CC as well so take it easy on me.

Im also not talking about schools like Stanford or Caltech, more like Washington, Colorado, or Oregon State

First of all, thank you for your service. I respect and honor people like you. Your personal narrative should be very compelling for the universities you listed. Good luck!