You can't 'retire' in the sense that you receive a pension with less than 20 years. Which means you were at least an E5 (you had to mess up a lot to retire as an E5). You are certainly higher than an O3 if you were an officer.

Presumably after 20 years you've also got other savings such as the TSP retirement account which the military matches 50% on (up to a certain amount only I believe). Your retirement payout can be based on your highest 3 years of service (you get to choose now), which are typically going to be the last few, which if much of that is spent overseas will significantly increase your retirement package.

You still won't be living in SF but you should be able to live pretty comfortably in a normally priced city as long as the retirement package isn't your only form of savings. Bonus points if you'er now 20 years into paying off your house as well.