I spent five years in the Army. My time was spent in the 82nd airborne, a year in Korea and then on my second enlistment I went into the Ranger program and was in the 3rd batallion at Benning. I can only tell you from my experience above with where I served that size and strength like we are talking about here on this website is out of the question.
It's all about endurance training. In the Rangers, if you have any size to you it's frowned on because they think you will slow everybody down in many ways. They want you skinny and fast. Your physical performance is how fast and how far you can run. Sure, they want you to carry lots of weight in your ruck sack but that is also endurance training.
If you want to prepare yourself for boot camp and other adventures you would be better off working on your pushups, situps, flutter kicks, lots of running, pullups and overall athletic drills without weights for what you will do in the Army.
I guess there are those that would have access to a gym and the time and energy to go there depending on what your MOS (job) is. If you are going to be a grunt you might as well give up the idea of being big and strong like you are thinking about. To try to do this or maintain what you have will be impossible. When I got out of Ranger training I looked like I had been in a WWII German concentration camp. Even then they thought I was still big so my reward when getting to Ranger BN was being assigned the ammo bearer for the automatic weapon, carrying the 60 and then being the breach man for compound assaults.
I was still constantly hauled into the medical clinic for "pinch tests" (skin fold measurements for bodyfat analysis) periodically just because my weight/height didn't measure up with their charts. This started at the MEPS station upon entry to the Army and continued all throughout. If you have any serious amount of muscle mass now you can plan on having the same thing done. They just simply don't like men who are muscle bound.
If you are going to be a medic in a cushy hospital assignment, a supply or office clerk or some other job where you might have a regular schedule with no time in the field or other strains on your body you might be able to pull of having the time to go to a gym, have access to more food and be able to recover from your training to have noticeable goals.
Good luck and have fun!