The Atlantis was a really big ship that Germany used during World War II to catch and attack other ships that were helping their enemies.
It was a secret ship that was disguised to look like a regular merchant ship, so nobody knew it was actually a military ship. It had lots of different weapons on board like guns and torpedoes that it could use to stop other ships from sailing around.
The crew on the Atlantis were trained to be sneaky and to hide from other ships when they needed to. They also had a secret room on the ship where they could hide prisoners that they had captured from other ships.
The Atlantis was very successful at catching and attacking other ships during the war. It ended up sinking over 20 different ships before it was finally caught by the British navy.