Cheat Mode
Add the "+set developer 1 +set sv_cheats 1" command line parameter. Press ~ during game play to bring down the console window.

Spawn item: give (item)
Full health: give health
Save game: savegame
Load saved game: loadgame
Get all items: give all
Ammunition: give ammo
Invincibility: god
Ignored by enemy: notarget
No clipping: noclip
Fly mode: ufo
Teleport to a specific map node jumptonode
Play indicated map: map (map name)
Suicide: kill

Play level of your choice
When in a Single Player game bring down the console with the "~" key, and type the following to play any level and mission you want.

Effect - Code

Play Mission 13: Kharkov 2 - map kharkov2
Play Mission 12: Kharkov 1 - map kharkov1
Play Mission 1: Bastogne 1 - map bastogne1
Play Mission 2: Bastogne 2 - map bastogne2
Play Mission 3: Foy - map foy
Play Mission 4: Noville - map noville
Play Mission 5: Bomber - map bomber
Play Mission 6: Train Bridge - map trainbridge
Play Mission 7: Sicily 1 - map sicily1
Play Mission 8: Sicily 2 - map sicily2
Play Mission 9: Trenches - map trenches
Play Mission 10: Ponyri - map ponyri
Play Mission 11: Kursk - map kursk