Let's see if I have this one from memory...
There are several possible cases involving LRM indirect fire and spotting.
1) There is a spotter with no electronic gear and a shooter with LRMs.
2) There is a spotter with TAG and a shooter with SG-LRMs
3) There is a spotter with TAG and a shooter with SG-LRMs and both members are part of a valid C3i (NOT standard C3) network.
In ALL cases, the spotter must have a valid LOS to the target, and the shooter may not have a valid LOS to a target at all (so you cannot fire indirectly over a single hex of heavy woods, as the shooter does have a valid - if obscured - LOS to the target). LOS has a maximum range of 60 hexes (this is a rule from previous editions that was never superceded by current rules - seriously, folks, max LOS range isn't in TW - and therefore still applies as per Catalyst policy).
Case 1) Calculate regular shooting from the LRM-carrying unit, but ignore terrain. Gunnery+Range+Target's Movement Mod + Attacker's movement Mod+any damage-related penalties. Additionally, add a +1 penalty for firing indirectly. Finally, add the spotter's movement penalty to weapons fire (so if the spotter Ran, add +2). The sum of these factors is your total to-hit TN. If the spotting unit makes any attacks that turn, those attacks suffer a +1 penalty, AND the indirect fire penalty suffered by the LRM-carrying unit becomes a +2 instead of +1.
Case 2) The spotter must first successfully attack the target that turn with its TAG unit (this happens PRIOR to weapons fire). if the TAG hits, a lock is established. Calculate regular shooting from the LRM-carrying unit: Gunnery+Range+Attacker's Movement Mod+any damage-related penalties. Ignore terrain and the target's movement modifier. There is NO penalty for firing indirectly, and the spotter's movement modifier does not apply. There is no penalty for combining TAG-assisted spotting and shooting regular weapons by the spotting unit.
Case 3) The spotter must first successfully attack the target that turn with its TAG unit (this happens PRIOR to weapons fire). if the TAG hits, a lock is established. Calculate regular shooting from the LRM-carrying unit: Gunnery+Range+ Attacker's Movement Mod+any damage-related penalties. Ignore terrain and the target's movement modifier. There is NO penalty for firing indirectly, and the spotter's movement modifier does not apply. Finally, the range penalty is calculated as though the firing unit was the spotting unit; if the spotting unit is 7 hexes away, the "effective" range is "short". Minimum range penalties do not apply unless the firing unit is actually within 6 hexes of the target, and the normal maximum range of the LRM attack still applies. There is no penalty for combining TAG-assisted spotting and shooting regular weapons by the spotting unit.
Clear as mud?
