This mod is an extensive modification of the campaign layers so it does indeed alter the Campaign, magicsub.
This mod is not for use with your Career mode. You would find yourself in an empty world with only your own u-boat and the harbors!
It is meant to be used for individual missions, primarily multiplayer but it works very well for single player missions if the maps are properly done.
Also, as SWCowboy has said, it is great for modders to test their work by further reducing the loading times and allowing them to test their skins, units, environments, and GUI mods more rapidly. Good one there, SWC!
Thanks for the compliment, danlisa. I hope you will enjoy using either mod for mission play, mission creation, or mod testing.
You're right about BBW. I think I may be related... he looks like a long-lost brother!