Coven Compass

The Coven Compass (カヴン＝コンパス) is a Mobile Fortress, operated by Witches.

Etymology
A usually refers to a group or gathering of witches.

Appearance
The Coven Compass is a giant disk of stone 200m in diameter and 10m thick. The top of the disk has sharp lines running in each direction from the center, resembling an actual compass. Dozens of ropes hang down loosely from the underside.

Principles
The fortress hovers about 20m above the ocean and has several countermeasures to prevent anti-flying spells from bringing it down.

On top of the fortress is a device designed to fire a large-scale flash spell which can be used to "fry" invaders. The fortress also possesses the capacity for long-range bombardment, with an estimated 'effective' range of approximately 330km.

Battle of islay
When the coup d'état was initiated, the Coven Compass, near Islay, was one of the many sites that were attacked by the knights and a battle ensued between them and the witches stationed on the fortress. Following Smartvery's suggestion concerning how the Curtana Original only provides the knights with power within the UK's borders, they travel just outside the border, creating a standstill between them.

Battle of Buckingham Palace
The fortress was later used by the witches to launch a long-range attack on Buckingham Palace. The tremendous power of the blasts was augmented by shots from Princess Villian's bowgun into a destructive stream of water and a barrage of golf ball-sized spheres.

Trivia

 * The actual full range of the "flash attack" from the Coven Compass was never directly stated, however Smartvery mentioned that 500 kms was a little bit more than 1.5 higher than the actual range of the weapon, meaning that 330 km is only a reasonable estimate born from that comment.