The "Demon Sword of Paracelsus" was a large experimental rail cannon developed by the U.S. military. This cannon was installed by a U.S. Army Special Forces team in order to counter any B.O.W. threat the team might face, in Incineration Disposal Plant P-12A's power plant near the end of the Raccoon City Destruction Incident. Hooked up to the plant's backup electric generator, the cannon draws energy from the three large batteries inserted into the generator. As a safety precaution, these batteries are ejected after a particularly large energy drain (such as that used to power a tank-sized electromagnetic cannon) and must be reinserted in order to use the cannon again. The cannon cannot be aimed in the state in which it is found, and enemies must be lured in front of it in order to engage them.
Jill Valentine uses the reactivated rail cannon to unlock the emergency escape door by overheating the gun. However, Nemesis reappears, so she used it to finish off the otherwise indestructible pursuer before escaping via helicopter from the junk yard behind the power room.