1st: A machine-gun bunker, nearly immune to AT4, very resistant to grenades, some camouflage, minimal exposure to enemy fire.
2nd: A standing bunker, nearly immune to AT4, highly resistant to grenade, camouflage, very minimal exposure to enemy fire, with a ramp so you can duck out of sight quickly by simply walking backward
3rd: No-roof so you can easily deploy at4s and grenades. Less protected than the other two bunkers, but with much greater visibility.