These two pages explain it well:
"How to Use ""Who"" and ""Whom"" Correctly (with Examples) - wikiHow"
Grammar Girl : Who Versus Whom :: Quick and Dirty Tips ™

who -> subject -> he/she
whom -> object -> him/her

E.g. Who/whom did that to me? (He did.../She did... -> therefore it's 'who')
Who/Whom are you talking to? (I am talking to him/her -> therefore it's 'whom)

As for the other question: "No matter how targeted the strikes or how sophisticated the weapons (ARE), ...."
In that context, you always use 'are' vs 'is.' If you use 'is' then the word (object) must be singular not plural. So, 'or how sophisticated the weapon IS, ..." The verb is/are usage depends on the singular/plural form.

If you take the entire sentence (as a whole), you will notice the verb "ARE" is used before the sentence is completed so you don't have to use ARE in the first part before the comma.

I hope that helps.