Cut the volume, cut the isolation crap, keep the intensity high.
2-3 sets of quad dominant, squats or front squats (work on keeping the weight on the bar, don't go lighter with higher reps or anything).
2-3 sets of hip dominant, RDL's or something similar, same scenario. Keep the weight on the bar, drop the volume.
Maybe a little bit of extra work like 1-2 sets of isolation stuff or unilateral leg work at another point in the week. Tough to organize without knowing how your week plays out in terms of training/running.
That will help maintain the muscle/strength for a fair amount of time.
At this point in time you shouldn't really expect to be putting on lots weight or anything. Concentrate more on maintaining the strength/mass you have acquired and when you can switch emphasis from running back to lifting you can start to increase the volume and such again.
It would also help to see your whole workout of course. And food is important. I don't know if you get to really choose how much/what you eat in the Marines, but that much running can put you in a significant caloric deficit and start to mess with recovery.