Bunker Cluster

The Bunker Cluster (バンカークラスター) is a cluster munition warhead developed independently by England that releases hundreds of explosive shells that are made to pierce into underground weapons. So fearsome is the weapon that under the influence of the Roman Catholic Church, the European Union forced England to sign a treaty to ban the weapon.

The weapon was later used during Carissa's coup, the British Halloween, for the first time since the ban, most famously in the Battle of Buckingham Palace.

Principles
Developed using technology original to England, the warhead is often equipped on cruise missiles, allowing for a quick delivery of the warhead to its destination as it is fast enough to near Mach 5 at low altitude, not taking even a minute to travel 1000 kilometers.

When used, the warhead spreads around 200 special smaller shells that are made to piece a military shelter 50 meters underground. The detonation depth of these shells can be timed however. The warhead is powerful enough blow away an area with a radius of 3 kilometers in every direction.

Treaty
Several years prior to the British Halloween, with the influence of the Roman Catholic Church, the European Union adopted a treaty that specifically banned the weapons the UK had been developing. The country's nuclear weapons were banned, while France were not only able to keep their nuclear weapons intact but had received all of the United Kingdom's nuclear weapons under the treaty. The official reason given was because as France would be the sole possessor of nuclear weapons within the EU they would therefore have the technology needed to safely disassemble them. Moreover, the ban also included the Bunker Cluster warheads, though that didn't stop the country from continuing its development.

By the start of the British Halloween, several warheads had already been developed and were ready for use by the military.

British Royal Family Arc
In a response to the Eurotunnel bombing, Carissa has a destroyer armed with Bunker Clusters deployed to the Dover Strait in order to threaten France by aiming it towards the Versailles Palace, where the Maiden of Versailles resides.

During the Battle of Buckingham Palace, following the destruction of the Griffin Skies, Carissa orders the destroyer Wimbledon to launch a cruise missile with Bunker Clusters towards Buckingham Palace. Seeing the extensive damage that it would cause, not only on Buckingham Palace but in a considerable part of London as well, Kanzaki Kaori tries to use a large defense barrier with a 3 kilometer wide radius to block the missiles. Carissa later attacks her as she tries to create the barrier, though she is able to dodge it but the construction of her barrier is delayed. Kanzaki tries to create the barrier again. However, it is too late, the warhead splits and is able to get through the holes of the unfinished defense barrier. In spite of this however, 200 of the missiles exploded prematurely because of the barrier, sparing London. As the missiles were set by Carissa to detonate 5 meters underground, the missiles bury themselves into the ground before exploding in Buckingham Palace. Magicians present on the scene would later use defensive spells to weaken the destruction caused by the missiles that got through.

Before Carissa can order another attack with a Bunker Cluster-equipped cruise missile, Riméa uses a mass communication spell in London and reveals Carissa's true motives for her coup and pleads to those who hear, specifically the knights and the Knight Leader, to save her. The knights, who have recovered from Carissa's "punishment", and the Knight Leader answers Riméa's call as well, using his magic to prevent another Bunker Cluster attack on them. He orders the knights to assist the fallen Anglicans while he engages Carissa in battle. Carissa tries to fire several Bunker Cluster missile attacks on Buckingham Palace in order to bypass his magic but is stopped by Acqua of the Back destroying the antenna that is used for military transmissions.