When you are sitting at the sonar station, and you rotate the listening head around to where a "normal" ship is, there is a little green bulb above the dial that will light up when there is a sound contact. When you get relatively close to the correct bearing, you will hear the thump-thump of the engine and blades in the water. If however, you have an NKLSS_Hansa, or the KGHAP_Hansa, you will not hear nor see them if you are at the station. You will see sonar lines on the NavMap though... The old problem with some of the ships was the light would be lit green, but the player could not hear them while at the sonar station...
It sounds like you have the game installed in the Program Files folder, and as such, Windows will "protect" you from yourself and the world, and rollback any and all such "un-authorized" changes. You need to either copy the game into a folder you make yourself, outside of the Program Files folders (such as "C:\Games \Silent Hunter 4"), or re-install it there. If you have the Steam copy of the game, it is usually easier to re-install Steam into a "Games" or some-such folder, and put SH4 below that. If you have a 2nd hard drive available, then you can create a 2nd Library folder under Steam, and install SH4 there...
We did not make such modifications, especially to a Gato. We made Mark 10s available to your boat from late December 1941 to the end of 1942, but they cost you money. We have been trying to get the S-Boats to automatically load-up with the 10s, but have failed thus far, so if you have a Gato doing that, ~WE~ want to know ~YOUR~ secret...
- Now, say you have a Pearl boat, and if when you re-fit at Midway enroute, you topped-off with Mark 10s... those will stay with you each time you re-fit with a partial load. But when you end patrol, that should then cease... What mods do you have enabled? and have you added to or taken mods out during your career?