Enter one of the following passwords to unlock the corresponding MPO+ soldier:

Have a saved game file from Metal Gear Solid: Portable Ops on your memory stick to unlock Boss Rush mode.

Find Johnny from Metal Gear Solid, Metal Gear Solid 2, and Metal Gear Solid 3 as a random prisoner in Infinity Mission to unlock Johnny.

Successfully complete Infinity Mission on the Easy difficulty setting to unlock Naked Snake.

Successfully complete Infinity Mission on the Medium difficulty setting to unlock Old Snake.

Successfully complete Infinity Mission on the Hard difficulty setting to unlock Raiden.

Successfully complete Infinity Mission on the Extreme difficulty setting to unlock Roy Cambell.

Knock out the first Tengu Soldier you encounter, and carry him back to the truck unconscious to unlock the Tengu Soldier as a playable character.

Find all 68 entries on the soldier list, then successfully complete an Infinity Mission round to unlock all sixteen Taunts.

Bump your comrade's box while there is an enemy knocked out. The screen will turn black for a moment, and the "Soldier Captured" message will appear. This works with multiple enemies; you can pile them high (for example, on Special Stage 16).

Enter "TTOGZWSREYD" as a recruit password to unlock Arms magazine Nile Crocodile soldier.

Enter "YLFSSVBCDLGO" as a recruit password to unlock Dengeki PlayStation magazine soldier.

Enter "ZKUJZUYXJUH" as a recruit password to unlock Famitsu magazine soldier.