[difool2]

Download S3D and edit scene.dat. In Sky>EnvSim>FogDistances there are four array items, one for each visibility (fog) level. You need to edit CloudRelativeZMin and CloudRelativeZMax to sort out your problem. Bear in mind that the clouds are a flat texture laid on a big dome and, for fogging purposes, Z is measured on the horizontal plane only; the clouds directly above your U-boat are at Z=0 and the clouds on the horizon are at approximately Z=0.9.
HTH
OLC

Thanks for the tip.