UNN Heisserer was a PT Boat of unknown class within the United Nations Navy. It was assigned to be part of the UNN's Jupiter Fleet.
Season 3 Edit
The Heisserer is one among the many ships within the Jupiter Fleet described by XO Shaffer and Lieutenant Mancuso as loyal to Admiral Souther over Fleet Admiral Nguyễn. When sailors loyal to Souther briefly take over the UNN Agatha King, the Heisserer is one of the many vessels that responds to Souther's emergency broadcast from the bridge and proceeds to withdraw from the conflict opposing MCRN vessels.
However, when Fleet Admiral Nguyễn and forces loyal to him retake the UNN Agatha King and kill Souther, it is revealed that the Heisserer, along with Jimenez were not responding to his new demands to return to the fleet. After the Agatha King's weapons officer refuses to open fire on a friendly ship, Fleet Admiral Nguyễn personally takes control of the weapons system, and demands that the other ship Jimenez return to the fleet or it will be fired upon and treated as a deserter. When the ship continues to ignore his demands, he launches a single missile which destroys the ship. It is likely that Heisserer was then one of the UNN ships that returned fire upon the Agatha King.