Enter at the password menu
Password--> Effect
JUNKER--> Cunningham
Hunter-n --> Null
LQ.N2 --> Python
ERBE --> Gene
PK +ESP --> Ursula
THE-L --> Elisa
E.APPLE --> Eva
PM-EMS --> Paramedic
DARPA-1 --> Sigint
R.R.R. --> Ocelot
1+2-3 --> Zero
IVN =RV --> Raikov
T.F-ACID --> Teliko
MGA2VE --> Venus
!TRAUMER --> Ga Ko
SATURNV --> Sokolov

Unlockable characters
Unlockable--> How to Unlock
Raikov --> Place spies in Western Wilderness before clearing the Guard House mission. Afterwards you should get a report of a handsome prisoner being held there.
Cunningham--> Beat Cunningham on ANY difficulty by stamina kill and beat the game before January 1st 1971 in game. You get him after you make a new game.
Null--> Kill Null by stamina kill or HP kill when you face him twice and beat the game. You get him after you make a new game.
Python--> Kill Python by stamina kill.
Elisa--> Get a Medic level of 80.
Major Zero --> Have a MGS:DGN game save on your psp's memory stick. (Second Playthrough only)
Teliko --> Have a MGA game save on your psp's memory stick. (Second Playthrough only)
Venus --> Have a MGA 2 game save on your psp's mamory stick. (Second Playthrough only)
Para Medic --> Contact her on the radio on the Comm Tower stage. She will later need to be resceud in the hospital stage. Place spies in the hospital.
Sigint After Snake is captured and rescued you can contact Sigint on the radio at the Comm stage. He will need to be rescued in the town.
Gene --> Recruit 200 soldiers and stamina kill Gene all in one playthrough.
Sokolov --> Give the Saturn V blueprints to Sokolov