Greetings!

I have been regularly on this site over the years, and have a question that has been a 'how did they do that' in the back of my head.

For example, U-2540 was scuttled in May 1945. In June 1957 it is raised and re-commissioned.

How does one scuttle a U-boat, leave it submerged for 12 years, and make it a worthwhile effort to make it serviceable again?

Do they only flood the ballast tanks and leave the interior airtight as a deliberate act?

Based on the images I have seen of other flooded boats the interiors are a complete write off.