The one piece of lingo I will often use is the word "crossfire." When it's not your turn, your scouts, shocktroopers and tanks units will automatically open fire at any enemy units who take action within their line of site and range of fire. This concept is called crossfire.
We'll begin with the Scout class. Both main characters Alicia Melchiott and Welkin Gunther (when he's on foot) are scouts. Scouts come equipped with a rifle, one grenade, and a med pack. Their rifles have above average accuracy and range, and shoot five times in a single salvo. Scouts have significantly more AP than any other class, meaning they can often travel farther with one Command Point than most other classes can with 2-4. Some scouts, like Alicia and Aika, even have the Double Movement Potential, which has a chance of completely refilling their already massive AP bar once it's been depleted.
In a game where versatility goes an incredibly long way, the Scout class will be your bread and butter, as they work well independently and in groups, and can fulfill a variety of tasks. As defenders, scouts are able to provide an effective first line of defense with their long range crossfire. As attackers, they're able to clear out weaker enemies to make room for shocktroopers, as well as perform reconnaissance functions, spotting enemy units to help you plan the rest of your phase.
At level 11 your scouts become Elite, and gain access to underslung grenade launchers. These are the same grenades that you throw, but now you have an option loading the grenade into this launcher, to catapult it much farther. The grenade launcher has an extremely high and steep firing arc, which means you can blindfire it into high places to root out hidden enemies, and also launch grenades behind enemy lines with relative ease.
If scouts have one weakness, it's that they're really only decent fighters, until you unlock grenade launchers and high accuracy rifles. Their attacks lack bite, and as the one of the flimsier classes in the game, they can't take much heat. However, much of this can be temporarily covered for by exploiting the Orders available to you. Scouts show more progression than arguably any other class, and endgame Scouts are a force to be reckoned with.
I strongly recommend deploying at least a couple scouts (including Alicia) in pretty much every mission. They're fast movers and extremely versatile.
Shocktroopers are the guys you call in when you just need to storm a place. No subtlety, no mercy; they're gonna go in, guns blazing. Shocktroopers are the hammer. They are the solution.
Shocktroopers come outfitted with a machine gun, one grenade, and a med pack. Their machine guns are deadly against infantry and even effective against tanks (if fired at the radiator), but their accuracy and power drops off sharply past medium range. They fire in large, 20-round bursts. At level 11, your now-Elite Shocktroopers gain access to flamethrowers. Flamethrowers are wonderful for multiple reasons. One, they completely ignore cover, which means you can kill enemies sitting behind cover, without having to use a grenade and risk blowing both them and the sandbags away (or even a smoke cloud, if you're using one). Secondly, the flamethrower is deployed in an extremely wide, sweeping arc, which makes it very easy to hit multiple enemies in one stroke. Unfortunately, the flamethrower is only effective at melee range, so you're gonna have to right up next to your target to use it.
Shocktroopers are the second toughest class in the game, after Lancers. They laugh at scout bullets, and can certainly take some punishment, but they do fall prey to mortars and tank shells. Shocktroopers also make excellent camp defenders, as any foot soldier foolish enough to approach them will meet a blizzard of machine gun crossfire.
Some classes have a more prominent trend in potentials than others. With shocktroopers, you may find that the happiness and effectiveness of any given unit is directly proportional to how much trouble they're in and how many enemies there are to gun down. Shocktroopers' positive potentials tend to deal with reducing incoming damage and increasing outgoing damage. Jane's Imp Hater potential gives her a boost against all Imperial soldiers. The more guns there are trained on Vyse, the more likely you'll get his Challenge Lover potential.
The most crippling factor holding shocktroopers back is their lack of accuracy and range, combined with their only moderate amount of AP. Without some foresight, it's very easy for your scouts to outpace your shocktroopers and end up carrying the mission on their own, especially as you approach level 20.
Still, shocktroopers are the second most useful class in the game purely for their killing power and hardiness. It's always a good idea to at least deploy Rosie, whenever possible.
You'll find that in most battles, you can get by with just scouts and shocktroopers. Now we're looking at specialist classes. Lancers are who you call when you need firepower with a lot of kick. They're who you call when you need some fireworks. They're a fearsome class of soldiers that look like they could gut you like a fish with their massive anti-tank lances (which are basically fancy looking RPGs). The lance is the only weapon a Lancer carries, alongside a med pack. Their anti-tank rockets have the second longest ranges in the game, defeated only by sniper rifles and possibly the Edelweiss.
Lancers have only one real purpose, and that is to destroy tanks. At level 11 you have the option of equipping them with portable anti-personnel mortars instead of anti-armor rockets, but there aren't a lot of situations where you'd want a mortar where one or two grenades wouldn't also suffice. Their lances are only slightly less potent than the Edelweiss's own shell cannon, and at half the CP. Lancers are also the sturdiest class in the game, shrugging off both bullets and explosives. This makes them affective as decoys and frontline combatants.
However, the benefits largely end there. Lancers have the second least amount of AP in the game, meaning you have to make every step count. They also don't provide any crossfire at all due to their anti-tank lances having limited ammo, which cripples their use as defenders. The biggest issue with lancers however, is their terrible accuracy. Though their rockets have a fairly high effective range in terms of damage, you're going to have trouble hitting anything beyond mid-range distance. Even endgame and royal-class lances only achieve C-rank accuracy.
Furthermore, the Lancers' job is often rendered unnecessary by other classes, who can simply maneuver around tanks to hit their weak spots. It's only in the case where a tank is sitting on an enemy camp that lancers really have a use, as there often isn't room to run around to their back before you end up riddled with bullets. Like snipers, I'd recommend only fielding Lancers mid-operation, as you need them. Largo might be worth having around solely for the extra Command Point, though.
Engineers are an interesting class. They can wear a lot of hats if necessary, but they also have a lot of drawbacks. Engineers use the same loadout as Scouts (a rifle, grenade and med pack), with the addition of an engineering tool, and three grenades instead of one. They're able to refill the ammunition of nearby units, repair tanks and sandbags, and disarm mines. Engineers also have the second most AP in the game, after Scouts.
Engineers have poor combat stats across the board, sharing 1st place with the Snipers as the flimsiest class in the game, and there are almost no individuals in this class who don't have more negative potentials than positive. As such, while they do carry weapons and quite a few grenades, they should almost never be used in direct combat. Instead, you'll find the Engineer's strengths to be in field support; running around, making sure everyone's got plenty of ammo and using their extra grenades and toolkit to clear out obstacles.
Finally, engineers share a mutually beneficial relationship with tanks. The tank provides solid cover for the engineer and protects him/her, while the engineer keeps the tank stocked with ammo and running smoothly, and if necessary, can defend the tank's weak spot.
If you're going to be doing an operation that's heavy on tank, lancer or even sniper participation, you might consider deploying an engineer. Otherwise, don't bother.
Snipers are highly specialized units. They come packing only their signature sniper rifle and a med pack. They have extremely low health and defense, and the least amount of AP of any class. Unless you count tanks, they're also one of the smallest classes, consisting of a mere handful of individuals. Their sniper rifles are deadly to infantry and to any tanks who unwittingly expose their backs, and have the longest range in the game. A sniper can kill in one shot from all the way across a map.
However, snipers are by far the most useless class in the game, at first. Because accuracy is paramount to their effectiveness, anything less than A-rank accuracy on their weapons is unacceptable, but it's a while before you're able to upgrade your sniper rifles enough to achieve that.
Even with the best rifles in the game however, it requires a certain kind of situation to merit deploying snipers. For example, if you don't have the high ground, or if a battlefield is littered with obstructions and obstacles, you might as well not bother.
Under the right circumstances however, snipers can provide valuable support to frontline units. They can finish off units you weren't able to kill in one burst with a scout or shock trooper, and also straight out murder more troublesome enemies from far away with headshots. Throughout the game you'll occasionally find high towers that provide an excellent view for snipers. My only caution with these however, is that you step down from the tower after you take your shot, as enemy tanks have a stubborn tendency to try to nail any snipers they spot in towers. Given a tank cannon's accuracy, it's extremely unlikely they'll hit, but the AI will keep at it until a shell flies true, and that will spell bad news.
It's easy to forget that tanks are a separate class, because on your side there are only two of them: your main tank, the Edelweiss, and later on the Shamrock.
The Edelweiss is the backbone of your squad. It's your most powerful unit and your most important one. Like all tanks, the Edelweiss is completely immune to gunfire that isn't directed at its ragnite radiator in the back (and even then, nothing short of concentrated machine gun fire will do much). Explosives--shells, lance rockets and mortars--are the only thing that will damage its armor. The Edelweiss is outfitted with three primary weapons: a shell cannon, a machine gun, and a mortar.
The cannon is of course used against enemy armor. Naturally, the armor piercing shells it fires are also lethally effective against all infantry short of lancers--you can even score headshots with them for extra damage--but it's far too inaccurate to rely on for that. The cannon has a long range, and is cable of destroying certain environmental objects, such as sandbags and low integrity walls. It doesn't do any splash damage, so you do need to actually hit your target. The cannon's effective range is a little farther than the average rocket lance, but its relatively low accuracy means you might want to get closer for more precision.
The machine gun's short range and small magazine stops it from being a compelling offense weapon against infantry, but it will make most foot soldiers think twice before approaching the Edelweiss, especially because it is capable of providing automatic crossfire.
The mortar will be your primary offensive weapon against all infantry. You can use it on enemy tanks as well, but there's no reason to do that when you have the cannon. The mortar works just like a grenade, except on a much larger scale. The explosion is larger (and thus the splash damage radius is more substantial) and the damage is greater.
Later on the Edelweiss gains access to smoke shells. In practice, they work similarly to the mortar, except instead of inflicting mass destruction, they kick up a very large cloud of smoke. Smoke shells are delightful for a number of reasons, not the least of which is the awesome visual effect you experience while present in a smoke cloud. The primary effect you get from smoke clouds is invisibility. Being in a smoke cloud is like crawling in grass in that it you are impossible to see unless someone walks right up to you. This has a couple of benefits, but the main one is that it makes you immune to crossfire. This means you can fire a smoke round into an area or junction that might otherwise be a kill zone, and allow your units to pass by safely. It also makes it easy to snuff out enemy camps, firing a smoke round right into the camp, and then sending in soldiers to kill the defenders while they're blind. There are a couple of things you have to keep in mind with smoke rounds, however. Like mortars, you have limited ammo per phase. You can only fire one shell in one phase, and unlike every other weapon with limited ammo, engineers can't restock your smoke shells. Furthermore, smoke clouds affect everone, not just your targets. Once inside a cloud, you're invisible to guys outside and inside, but you yourself also can't see more than a couple feet in front of you, which also means you can't provide crossfire. You should still have the advantage simply because you're the one who fired the smoke round, and thus hopefully mapped out enemy positions before entering the cloud. Smoke clouds last for the remainder of your phase and the enemy's before dissipating, but any explosive that goes off in or near a smoke cloud will blow it away as well.
Your other tank, the Shamrock, joins the squad midway through the game. Commanded by a hearty fellow named Zaka, the Shamrock is smaller and more maneuverable than the Edelweiss, but also packs less punch and has thinner armor (though like all tanks it is at least invulnerable to gunfire). The unique thing about the Shamrock is that you actually have three options to choose from for its primary weapon; the standard shell cannon, a flamethrower, and a gatling. You can swap in between these three at any time in between missions.
Personally, I usually stick with the flamethrower. The Shamrock's shell cannon doesn't have enough punch to justify using it over a lancer rocket, and the gatling is just silly, since you already have a standard machine gun and the flamethrower is a better anti-personnel weapon anyway.
Tanks are extremely powerful and versatile. They can move a fair bit each turn (more with upgrades), they are effective against every unit in the game, and they also provide excellent field support, able to provide cover for soldiers moving in convoy formations. The Edelweiss is also the broadcasting beacon for your Orders function; without it, you can't activate Orders.
However, they are not without drawbacks. The most prevalent negative is the fact that if the Edelweiss (and by extension, the main character Welkin) is destroyed, you automatically lose the game. This is constantly something to keep in mind before taking action with the Edelweiss. The second issue is that whereas it only costs one Command Point to deploy any footsoldiers, it costs two to use a tank. This doesn't seem like much, but when you have only a handful of points, use of your tank can be a costly venture. Operating two tanks on the field is a significant drag on your CP.
Tanks have a moderate amount of AP, like shocktroopers. However, unlike infantry, it costs AP just to turn around in a tank, which means you want to constantly keep in mind whether enemies have access to your posterior. A tank's movement can be crippled by destroying its secondary health bar, which represents treads. Loss of its treads will not destroy a tank, but it will leave it with almost no AP to move around with.
Ironically, the smallest class ended up getting the longest section. You won't have a choice on whether or not to deploy the Edelweiss or, when it is introduced, the Shamrock. They're always deployed, unless story circumstances dictate otherwise. Personally, the CP cost is too high for me to consistently include a tank--much less two tanks--in my strategies. I prefer using foot soldiers most of the time. However, it still pays to at least keep the Edelweiss running with your troops sometimes, if only for its field support capabilities. The Edelweiss's smoke shells and heavy armor allow it to provide plenty of defensive support for your your infantry.