Put it in reverse: ATMs.

[Retry]

See above, you STILL cannot get 2 comparable LRM15s- IE they have Artemis IV- for the weight of a ATM12.  The ATM12 gets you 2 tons lighter and at least a crit less.

Comparable isn't synonymous with "has Artemis", the LRM series is perfectly comparable without it.  They can be nice to have but the twin LRM15s really don't need them (and they're arguably more flexible without it), so why try to shoehorn them in just because ATMs have it?

Last time I bothered to run the numbers of the ATM series, the only definitive advantage they had was at 0-3 and 22-27 range brackets.  4-9 usually went to the LRM array unless to-hit numbers happened to be unusually low for the HE rounds.  The LRM generally pulled ahead at 15-18 hexes too, unless the to-hit numbers were just awful (like 11s or 12s), and then the ATM's damage output was thoroughly uninspiring.

The iATMs, on the other hand, are a different beast entirely.

[MoneyLovinOgre4Hire]

Well, iATMs are terrifying.

[Colt Ward]

You are comparing weight on them and the ATM has integral Artemis IV, so for comparison yes, you have to give the launchers Artemis IV because that is what ATMs have standard.  LRMs mounting Artemis IV lose nothing in the ability to throw other types of LRM munitions, they just do not get the +2 bonus unless its Artemis IV ammo.

[Retry]

You are comparing weight on them and the ATM has integral Artemis IV, so for comparison yes, you have to give the launchers Artemis IV because that is what ATMs have standard.  LRMs mounting Artemis IV lose nothing in the ability to throw other types of LRM munitions, they just do not get the +2 bonus unless its Artemis IV ammo.

Artemis IV gives you roughly +21% extra damage on average during direct fire against targets without ECM, using the -20 column for a sample calculation.  Artemis IV is pointless on the Clan's -5 and -10 LRM launchers, has dubious utility on the -15, and has a slight benefit on the -20 in most circumstances.  You can compare damage output and tonnages just fine without integrating Artemis IV to the LRMs, and for a really rigorous analysis one would compare both an Art IV LRM and a regular LRM.

There is an opportunity cost in using the Artemis IV: that's a ton and a crit you can't spend for extra ammunition or CASE or heat sinks, per launcher.  Installing Art IV on one launcher means you have to install Art IV on all of that launcher types, even though Art IV is not efficient on small launchers, which generally shoehorns you into using larger -15 and -20 launchers.  Often the damage bonus can be useful (especially for IS launchers), but there's not a single design that can't become more flexible by scrapping the Artemis for ammo or other things.  (Not necessarily better, just more flexible)

[Colt Ward]

I absolutely agree and its why I do not like the system or put it on Omni loads I plan . . . BUT . . . its integral to the ATM system, and his comparison of 'You can get 2 LRM15s for the weight of a ATM12' is not an equivalence without including the system as part of it.

[mmmpi]

I absolutely agree and its why I do not like the system or put it on Omni loads I plan . . . BUT . . . its integral to the ATM system, and his comparison of 'You can get 2 LRM15s for the weight of a ATM12' is not an equivalence without including the system as part of it.

That's not how equivalence works.  As the others have suggested, you very well can leave the system off the 15's and still make a comparison between the two weapons, particularly if it's of limited value to the 15's.