Enter "JUNKER" as a password to unlock Cunningham. Alternately, defeat Cunningham on any difficulty setting by stamina depletion with the MK22 and successfully complete the game before the in-game date reaches January 1, 1971. Save after the credits and load the game. Get to a point where you can save the game. Save it, then exit the game completely. Restart the PSP, load your game, and you will get a message saying you have a new solider, which is Cunningham.

Enter "THE-L" as a password to unlock Elisa. Alternately, successfully complete the game with a "Medic" rating of 80. Play the game a second time. Save the game, exit, then load your game and she will join you.

Enter "E.APPLE" as a password to unlock Eva.

Enter "!TRAUMER" as a password to unlock Ga Ko.

Enter "ERBE" as a password to unlock Gene.

Enter "1+2-3" as a password to unlock Major Zero. Alternately, have a Metal Gear Solid: Digital Graphic Novel saved game file on your Memory Stick. Successfully complete the game, then save after the credits and load the game. Get to a point where you can save the game. Save it, then exit the game completely. Restart the PSP, load your game, and you will get a message saying you have a new solider, which is Major Zero.

Enter "Hunter-n" as a password to unlock . Alternately, kill Null by health or stamina depletion with the MK22 in both fights against him. Successfully complete the game, then save after the credits and load the game. Get to a point where you can save the game. Save it, then exit the game completely. Restart the PSP, load your game, and you will get a message saying you have a new solider, which is Null.

Enter "R.R.R." as a password to unlock Ocelot.

Enter "PM-EMS" as a password to unlock Null. Alternately, contact her in the Comm Building after Roy is feeling better from his malaria. She will offer to help. Place spies in the hospital and wait. She will eventually become a side mission to recruit.

Enter "LQ.N2" as a password to unlock Python. Alternately, instead of health depletion, use a tranq gun and stamina to deplete him. You will get a different intermission sequence and Python will join you.

Enter "IVN =RV" as a password to unlock Raikov. Alternately, after Snake is captured, do the missions as usual until the guest house. When you get to the guest house do not continue. Instead, place spies in town and wait. Do other missions until you get a report of a map. Retrieve the map and place spies in the wilderness. Keep waiting and eventually Raikov will need rescuing. Rescue him and proceed as normal.

Enter "DARPA-1" as a password to unlock Sigint. Alternately, after you rescue Snake and rercruit Para-Medic, go into the Comm building again. You will contact Sigint and he will offer to help. Place spies in town and eventually he will become a side mission.

Enter "SATURNV" as a password to unlock Sigint. Alternately, give the Saturn V blueprints to Sokolov.

Enter "T.F-ACID" as a password to unlock Teliko. Alternately, have a Metal Gear Ac!d saved game file on your Memory Stick. Successfully complete the game, then save after the credits and load the game. Get to a point where you can save the game. Save it, then exit the game completely. Restart the PSP, load your game, and you will get a message saying you have a new solider, which is Teliko. Alternately, place spies in the town. After awhile, you may get a report saying something about an alien and that there is a strangely dressed woman in the town. If you go to the town and capture (not meet, just knock her out) her, then you will unlock Teliko and some strange dialogue with Campbell.

Enter "PK +ESP" as a password to unlock Ursula.

Enter "MGA2VE" as a password to unlock Venus. Alternately, have a Metal Gear Ac!d 2 saved game file on your Memory Stick. Successfully complete the game, then save after the credits and load the game. Get to a point where you can save the game. Save it, then exit the game completely. Restart the PSP, load your game, and you will get a message saying you have a new solider, which is Venus.

Successfully complete the game with a "Technician" rating of 99 to unlock the Stealth Camouflage, which allows you to become invisible for a limited time.

Successfully complete the game to unlock the Extreme difficulty setting.

Have two weapons equipped. When you are close to running out in your clip, change weapons then immediately change back and your gun will be reloaded.

If you are looking for soldiers to recruit, the Soviet Patrol Base is an easy place to capture them all.

To recruit multiple soldiers at once, drag several enemy soldiers over to one of your teammates while they are hiding in a box. Then, call the prisoner evac frequency and your teammate will capture all of them.

During the mission before the Cunningham fight, the frequency for the first frequency door is scratched on the wall behind the guard that is posted in the room.

The frequency code for the doors at the Silo Complex are 145.75 for the first and 148.51 for the second.

Use Snake (he has the most health and stamina, and dying with him will not cause loss of your favorite soldier) with the 5.56x45mm Caliber Assault Rifle (M16A1 or XM177E2) and RPG7; Body Armor; and Medical Kit (L). Fire the M16A1 using the L lock-on button. Fire two or three magazines into his flying machine and there will be a minor explosion. He will drift downwards as his flying machine malfunctions. At this point, fire using the L lock-on again, but keep it to short bursts or single shots. Almost every shot will count towards taking down his life. Ammo boxes for the 5.56 rifle will continuously appear as you run low, and there is a spare M16A1 rifle as well. The rest is standard bullet dodging. Note: You can fire at the rockets he shoots later as his health gets low by shooting at them in First Person mode. Firing at the mines he throws will cause them to explode safely at a distance. Also, RPG7 rockets will count as a bullet hit on his health, and two or three consecutive shots will cause the flying machine to drift down faster, but there are no RPG refills during the battle.

The times which you can shoot him with a non explosive are when he is reloading, turned his back against you, still looking for you, or sometimes while shooting if you are lucky. The best gun for this is the shotgun. When you actually get a shot into him, it will knock him down.

CQC of any kind does not work on Null. If you try to punch, kick, or tackle him, he will slash you with his sword. He will also block any bullets you shoot at him. The only way to defeat him is to hit him in the back or wait until he reloads his gun. He fires three bursts before having to reload, and will shoot even if he cannot see you. Wait until the third burst, then quickly jump out and shoot or tranquilize him. Alternately, use any type of explosive, as he cannot block them.

When fighting Python, lock on to him with L and shoot him when he becomes visible through the fog. Make sure to continuously back up, otherwise he will lunge forward and knock you down with his weapon. It is also a good idea to plant the TNT with a soldier other than Snake. By doing this, when you begin the fight you will start as the character you planted the bomb with. Then if your character dies, you will have the option of selecting the next player to fight with so that you can save Snake to finish the job after Python has been weakened.

The best weapon to use against Python is the shotgun. It will knock him down and you can shoot him again before he gets back up. Additionally, the shotgun deals a lot of damage but does not require you to do any fancy moves.