Naglfar

Naglfar (ナグルファル) is a spell used to control ships, based on the ship of the same name from Norse Mythology which was constructed from the nails of the dead and would be used to ferry the hordes which would battle the gods at Ragnarok.

Etymology
Naglfar or Naglfari means "nail ship" in Old Norse.

Principles
As Naglfar was constructed from the fingernails and toenails of the dead, the spell requires nails from dead people. These are positioned in various places around a ship to turn it into Naglfar. After this is done, the user of the spell can control the ship remotely.

In the case of the marine prison hijacking, the prisoners made use of the fact that the prison was a ship carrying criminals, like Naglfar carrying the enemies of the gods, as a magic symbol to support the spell and assume control of the vessel. In this case, the Jeans Shop Owner also speculated that the spell might have made the prisoners into the Muspell as well, though it wasn't shown whether it did or not.

Background
An experiment regarding the Naglfar was carried out in Tynemouth. During the experiment, a wooden ship about 50cm long was successfully controlled remotely.

Toaru Majutsu no Index SS: Kanzaki
Prisoners aboard one of Necessarius's marine prisons made use of Naglfar in an attempt to hijack the submarine. By placing nails, from prisoners among them which they had sacrificed, in positions around the prison and making use of the ship transporting criminals as a magic symbol, they made the marine prison into Naglfar and took control of the ship from the Cape of Good Hope.

They attempted to run the ship aground in India, but after witnessing Kanzaki Kaori defeating the Víðarr Shoes Woman and being challenged by her, the prisoners surrendered their control of the ship.