Thank you for the answer of #2, that is helpful

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Regarding #1, my question is oriented toward the stage after which a ship is considered a wreck and rests on the bottom. In relative shallow waters 25 to 60 meters deep,(I.e French/English channel in some areas), if a submarine distance itself from a fresh kill for too long, then returns, the wreck has disappeared. The current did not move it away, the program erased it.
How can I, through modifications of datas in which files, make those wrecks to remain the entire mission or the entire campaign where they it hit the bottom?....
Thank you