For unlimited health edit Scripts\difficulty.txt and change the value under Damage0 from e.g. 0.17 to 0.0 for easy mode. The Damage0 values in line 2 and 3 are for Medium and Hard modes.
Shift - F11 and to load use Shift- F-12
After you cross the bridges with the tank destroy everything related to the sam. It's timed for the last part of the mission so make sure you've left yourself a good three minutes to complete your task.
When you enter the crashed ship don't try to kill any of the Breed. Let them kill you. You will find yourself in a Breed prison where you can make your escape.
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