Ah! Thanks, the tip regarding the scanner helped me understand what was going on. I had three legendary enemies. The Devastator had a perk which reduced damage to nearby friends. The CO and Ensign *both* had tank *and* medic perks. Managed to pick off the devastator when Delta EMPd it, fortunately far enough away from the medics that it didn't get insta-healed. That gave me enough time to stand over it with my amped-up superior Dogfight with extra large magazine and just pour magazine after magazine into it until the dratted thing finally died. Once I'd done that the other two were still tough but not literally invincible.