To strengthen up for the military you probably want to do a lot of body weight lifting- push ups, pull ups/ chin ups, crunches, flutter kicks(lotsa those!), bends and thrusts(not too many of those

), squats, and calf raises/ rockers. Those are just a few of mine. I personally prefer power lifting. I work out with an old crusty Recon Marine Sergeant Major so he's got a lot of fun exercises!
And do your good mornings!