It's a DOOM2-mod called "Return To Castle Wolfenstein II".
It has to be installed in DOOM2 via DOS-Box.
After that you have 5 files to use with Doomsday: r2char.wad, r2levels.wad, r2sprite.wad, r2stg.wad and wolf.deh
They work fine with Doomsday.
But if you rename these files, the mod doesn't work anymore!
For exemple renaming them to 1.wad, 2.wad, 3.wad, 4.wad and 5.deh.
However as long as the original names of these files are part of the renamed ones, it works!
Pretty strange! Any suggestions?