The Briefing Room in Missile Command Delta presents two separate puzzles involving a keypad, missile schematics, a colorful control panel, and hidden buttons.
The mandatory keypad puzzle and the optional bookcase puzzle can be solved by adjusting the red projection and correctly pressing hidden buttons following the red arrows.
For the bookcase puzzle, positioning the red projection correctly, reveals hidden buttons inside red circles among the books, which need to be pressed in the specified order to open a hatch.
On the keypad puzzle, the solution lies behind the missile schematic poster, and by following the numbers in the correct order, the code 3-5-8-8-7-5 can be obtained to progress in the game.