Payload is a cut Zombies mode from Call of Duty: World at War. The objective was to escort an unspecified payload  before the timer ended. Not killing enough zombies would've led to the session ending. A cryptic message at the bottom of payload.str suggests the reward would be to unlock something, possibly as the objective of the payload.
- REFERENCE OBJECTIVE
LANG_ENGLISH "Escort The Payload."
- REFERENCE TIMER
LANG_ENGLISH "Zombie Timer: "
- REFERENCE FAILED
LANG_ENGLISH "Mission failed. You did not kill enough Zombies."
- REFERENCE MASTER
LANG_ENGLISH "You have become the MASTER OF UNLOCKING!",
- The "Master of Unlocking" title is a reference to the Resident Evil series, where protagonist Jill Valentine is jokingly called this early in the first game whereapon it became a running gag within the franchise.
- A similar version of this is seen in the Gorod Krovi main Easter Egg where the player(s) escort both a Valkyrie Drone and a Russian Mangler Soldier to a specified area.