Well, in the vanilla game (that is to say, without the mod), the skills of the soldiers you use in the field only go up whenever you use them. So the more you shoot in burst, the better your guy gets at handling bursts and so forth, and the higher your skill is the more individual uses of the skill are needed to get one more point in it.
That’s a good idea in theory, but is a bad thing in practice because some of those skills are rarely used but still need to go up fairly regularly (such as the medical and engineering ones) and others are only used if you’re actually playing somewhat badly early on, but will screw you late in the game if you haven’t levelled them up - I’m mainly thinking of the interrupt skill here, but hit points also only go up if you do get shot, which you’re going to try and avoid :p.
So what happens is that early in the game it’s a toss-up whether your guy running into a room is going to get the drop on the nasty nazi lurking inside, and even if you don’t at the worst you’ll get a couple of pistol shots to the face or maybe a rifle shot. Survivable. Late game, if your interrupt doesn’t keep up, your guys will **always **get interrupted, quasi always with full auto mag dumps, and they won’t have the health to survive that.
So that’s not a lot of fun.
Meanwhile, the soldiers you don’t use and who stay at the base all level all their skills somewhat evenly so that they don’t get left behind and can be used as replacements in a pinch. The catch being that they’ll always be a couple levels behind the action guys, so rotating them around all the time is not ideal either.
Originally, the only solution was to grind skills on your guys basically, setting up camp in the wilderness then letting them all run around, hide/unhide/hide, plant mines then disarm them etc… over and over between missions. Not fun.
Thankfully someone came up with the skill watch mod which is essentially a script that runs along with the game and which, whenever one of your guys levels up, checks each of their skills, bumps them to the minimum the guys back at the base get at that level if it is below that threshold, or leaves them alone if you’re already better than average in that skill.
So that’ll let your scouts not get interrupted all the time, lets your docs use the better healing and buffing items and so on.
You can get it here.
I don’t recall off-hand if it’s needed in *Sentinels *(or if it even works with it) however - never played it all that much.