I used to be a civilian employee of the USMC, and was able to use the base gym for free. The setup was exactly as I expected, about a dozen shower heads in a U shape configuration with no dividers.
The only thing that caught me off guard was the number of guys that would just chat naked with their friends for really long times. I remember one instance where I had finished my workout and returned to the locker room where there was a group of guys just standing around chatting naked. I took my clothes off, grabbed my towel, took a quick shower, spent time in the sauna, showered again, and came back... The same guys were still there chatting naked.