There is a lot of information on indirect fire weapons to be found in the manual. However, it's quite spread out, so I thought it would be a good idea to concentrate all of it here in one place to get the whole picture. I also think it's quite important to point out the advantages that indirect fire weapons can provide if fired directly.
- Indirect fire weapons are marked with an asterix (*). Note that there might be some weapons around which you would expect to be indirect fire weapons but which are actually none (e.g. SAW, "Bargain of the Day" scenario, the AK-74/GP25 grenade launchers / 40mm HE (Indirect Fire) ammo --> it has no asterix)
- Indirect fire weapons can either fire with a line of sight on the target or without a line of sight on the target (see below). As a speciality, indirect fire weapons don't have their line of fire blocked by firendly troops (if they can see the target, the overhead fire still counts as a fire with LOS).
- Indirect fire weapons ignore the cover ("protection") provided by hexside obstacles (walls, fences, etc) and the cover the opponent gets for being at a higher elevation level. Indirect fire weapons might also ignore the cover provided by gullies/riverbeds, but I'm not sure (the wording in the manual is not clear, see p. 41).
Fire without LOS:
- Will not be used for opportunity fire
- does not suffer any range malus (normally, weapons that are fired over half their max. range suffer a *0.5 malus)
- *0.5 malus on effectiveness (for not seeing the target)
- scatters (up to 1 hex + 1 hex for each additional 10 hexes distance to the target)
Fire with LOS:
- Will be used for opportunity fire
- does not suffer any range malus
- no *0.5 malus
- no scattering
So, generally speaking, you should try to use your indirect fire weapons in a direct fire method (with LOS on the target) whenever it's safe/possible.