You'll need to choose the Skill Points option for the first time you do this in a province in order to access the option to reveal all weapon case locations, which is only available the second time you grab intel there. Either way, you'll get three options of things you can reveal in that province. Intel caches only need you to interact with them, but lieutenants require you to grab and interrogate them. To do that, just go to an occupied location and look for exclamation marks, which point to either intel caches or lieutenants. No matter what weapons you go for, gathering intel helps immensely, revealing all the weapon case locations in a region.
