OK, that explains it then. Someone else on here a few weeks ago had the same problem with telling the difference between their v1.3 and v1.5 Steam installs. It does sound like you are in the v1.3 folder instead of the v1.5 folder. Do you have two "Silent Hunter 4" or "Silent Hunter Wolves of the Pacific" folders under your "common" folder? I have Steam SH3 and SH5, but my SH4 installs are a Ubisoft Gold edition download, a Gold disk, and an original Wolves of the Pacific disk with a Ubisoft purchased download of the Uboat Missions add-on, so I am not familiar with a Steam SH4 install. But I am all-too familiar with dealing with a Steam game install. Let us know what your folder structure is like.
