My mate Joe made this map years ago. I have put it here so that we can always get hold of it to reminisce.
This is a Coop/SP mod.
There is basically a bunch of pillboxes and loads of guns.
1) Grab the guns.
2) Get inside a pillbox.
3) Open up the beastie pens before and opening up on the beasties.
Notes: Don't run this on a 486 because there really are a lot of beasties. Perhaps it will even give a modern P4/Athlon a run for its money.