At the main menu, press Triangle, Circle, Triangle, Square, Triangle, Circle, L1 + R1 to
unlock level select and all challenges. Note: There are two side effects after
using the level select cheat. First, stealth attacks no longer give you dog tags, which
means you cannot advance to a higher strike level. Get all the tags you need before using
the cheat. Secondly, when you save a game in which the level select code is used, the file
is now marked with an "X" just before the time and date.