Xcom 2 Long War Guide -

"You have two choices: Explosives or Flanking. Explosives destroy cover. Flanking negates it. You bring a Rocketeer or a Grenadier to shred the walls the enemy hides behind. You use your Assaults to run up the flanks and deliver point-blank devastation.

: You cannot just launch a mission immediately. You must "infiltrate" by stationing a squad at the site for several days. xcom 2 long war guide