You can expect around 20 lbs every month if you do rolling 72s or even a mix of rolling 48 and 72s.
For starters don’t work out too hard. See when you are in a fasted state your body is already in physical stress if you work out too hard your body may end up adding stress and secreting cortisol which would trigger insulin secretion, breaking your fast. Most people I have seen here do long walks which seem suffice. I’d suggest don’t directly jump into a 21 day fast. Start with one meal a day for a couple of days then you can switch to rolling 48s
I would say rolling 48s or 72s on snake juice would be the best. I find that 48s and 72s are best because it combines sustainability and quick results. The problem with long fasts is that it’s easy to yo-yo because there’s no discipline that a structured regiment will give you. Also with shorter fasts there’s a light at the end of the tunnel which is your refeed. If you want to do a long fast after doing 72s for a while just to get the last 10lbs off then by all means.
I’m down 33 lbs on a 22 day prolonged fast. I could lose even more if I were active, but I just sit around all day. You’re military, you should be disciplined. Go big or go home. If you exercise, just keep it light. Low to moderate weights if you lift. Steady state easy cardio on a bike or elliptical, or just walking all day is fine. No need to do any more than that.