The Mystic Chest can be used for storing ships while they are not being used. The Mystic Chest starts out being able to hold 2 ships, and can hold 1 additional ship for each level it is upgraded. Each upgrade costs 100 gems.

Mystical chest

  Fully upgraded, the maximum number of ships that can be stored in the chest is 21.

When a ship is put into the Mystic Chest, all weapons loaded onto the ship are also stored. The ship retains its level and all other characteristics.

Putting a ship into the Mystic Chest does not free up the crew to be used on other ships.