The crab submarine was a vehicle used by the Trade Federation's aquatic navy.
One such model was commandeered by Harro Ruuk after his on Maramere was destroyed by the Lok Revenants. Ruuk escaped the explosion in his vessel, and launched a desperate assault on Nym and his colleagues. Ruuk was defeated, and his submarine was destroyed, though Ruuk himself escaped in an escape pod.
The crab submarine was armed with two rapid-fire laser cannons, and four homing concussion missile launchers.