In the Data Vault, highlight the "S" logo that would typically allow you to access Dead Ops Arcade 2. Press and hold all four shoulder buttons on your controller. As you continue to hold those buttons, press X+Y on your controller (or the equivalent) and you'll bring up a secret menu, where you can enter cheat codes. Enter one of the codes below for the corresponding effect.

1. MANIFEST - Receive up to 100 Fabrication Kits.
2. DREAMLAND - Access "Nightmare Mode" without first clearing the campaign.