The pictures below identify each clue. Their printed numbers belong to reference matches: enter the four digits from your own game.
Upgraded gun: shoot plates 1 → 3 → 2 → 4.
Take the War Room key; open the center desk.
Explosive behind machinery; photo appears right of window.
DEFCON: upper far → Server → upper near → lower. Use Server teleporter.
Collect all four pictured codes; the screenshots show examples only.
Visual references: mmmrkennedy. Gameplay © Activision/Treyarch.