What is the Ark of Miriam in the novel, The Amazing Adventures of Kavalier & Clay?

The Ark of Miriam is the ship that is bought and chartered by Mr. Hermann Hoffman, who runs the TRA, the Trans-Atlantic Rescue Agency, a mostly one-man operation, with the assistance of Rosa Saks. Thomas Kavalier, Joe's brother is on the ship, when it is sunk by a German submarine.