Low-carb should be good for at least 3-5 lbs. of water weight in the first week or so. Since you're only 10 lbs. overweight to start, I wouldn't expect too much more than that just on LC alone. So you're probably going to have to do some old-fashioned calorie restriction and serious exercise, too.

Based on the photos I've seen of some reservists lately, I'd say 10 lbs isn''t a make or break deal; but I think those guys were all Army. How strict is USNR?