Lots of Navy in my family!

But mostly just a good deduction on information given.
Here's what I learned from my trainer. Instead of doing reps with the bands, like you would with weights, you repeat the motion for a set length of time. For example, a twist. Fasten the band to something stationary, hold the other end with both hands at arms' length, and twist--sort of like you were swinging a bat, except you aren't trying to knock anything out of the park. About 2 seconds per twist. Do this for one or two timed minutes per side to start. Same thing with other band exercises, like squats, biceps curls, leg extensions.
Most sets of bands come with an exercise book. You can use a lighter-resistance band or heavier-resistance band as needed.
I guarantee that this will get you sweating like an aerobic workout and will keep you from losing muscle mass as well.
Jay