How do you unlock weapons on Metal Gear Solid peace walker

To unlock weapons on MGS Peacewalker, you must build your R&D team to various levels. also, some weapons can be unlocked via story mode. Lastly, for those people who purchased the MGS Peacewalker PSP3000 Ltd Edition, You also receive a voucher for a FOX T-shirt (in-game) and a Stealh Gun 2 (CO-OP Only).