THUNDERBOLT-10 Nuclear-Propelled Plasma Turret

The THUNDERBOLT-10 Nuclear-Propelled Plasma Turret is a nuclear shaped charged-based anti-ship weapon developed for the UNSC Navy during the First Great War and War of Vengeance.

History
Development of ship-based weapons stalled after the age of space colonisation - the creation of a comparable navy required resources and infrastructure that simply wasn't available to mere pirates, privateers and insurrectionists, allowing the Navy almost two hundred years of naval dominance. When the Covenant attacked, the UNSC found itself in the unenviable position of having to field a fleet intended to support ground campaigns unhindered against a technologically superior fleet of warships. Progress was made even in the early years of the war, but in the end it all came down to a matter of technology - the Covenant had the advantage, and the UNSC wouldn't even come close to catching up for decades.

As part of Project EXCALIBUR, the Office of Naval Intelligence investigated a range of replacements and supplements to the standard Archer Anti-ship Missile and Magnetic Accelerator Cannon, eventually adopting a number of different types to fill extremely specialised roles in ship-to-ship warfare. These were designed to rely on more "powerful" nuclear or EMP warheads to lower Covenant shields first, leaving the ship vulnerable. Among these new weapons was the THUNDERBOLT-10 Nuclear-Propelled Plasma Turret, designed to deliver a massive blast to blow through Covenant shields, but without the long charging time required by MAC guns and with a faster rate of fire. These weapons systems proved devastating against Covenant ships, and prototypes mounted on warships amazed both their designers and the Covenant when two THUNDERBOLT-equipped ships obliterated two Covenant Frigates at the Battle of Earth without a single MAC shot or missile fired. By the time of the War of Vengeance, the THUNDERBOLT-10 Nuclear-Propelled Plasma Turret had become one of the standard ship armaments, though ONI had restarted Project EXCALIBUR to devise improvements to the weapon system. With the development of arsenal ships and the Multi-Stage Missile, however, they have become somewhat redundant weapons when UNSC warships can now destroy enemy ships at ranges of over two million kilometres. Despite this, they remain standard ship armaments should a ship exhaust its missile complement, and they saw service against the Governors of Contrition during the Second Great War.

Design
The THUNDERBOLT-10 Nuclear-Propelled Plasma Turret works on the principle of a "firecracker under a tin can": An Teller-Ulam type nuclear device was encased in an shell of x-ray opaque uranium, with a single hole in the top of the case. This whole assembly is then encased in a "cartridge" of the UNSC's incredibly strong and heat-resistant MITHRIL armour. When a target was acquired, the cartridge is loaded into the turret's firing chamber. Upon a computer command, the nuclear device is detonated, and the uranium forces the x-rays to exit from the hole, and they are forced into a large mass of beryllium oxide. The beryllium transforms the x-rays into a massive blast of heat with temperatures comparable to those of a G2-type star. Perched on top of the beryllium is a thin plate of a low atomic number metal (the exact type of metal remains classified November Black). The blast of heat turns the metal plate into a star-core hot spindle of plasma that is blasted straight into the target with a yield of two hundred megatons and enough force and heat to blow through fifty metres of Covenant shipbuilding alloys. After firing, the MITHRIL cartridge is ejected from the firing chamber into space and another is loaded within two seconds. Compared to modern missiles, however, they have an extremely short range of only forty thousand kilometres, and are typically only used if a ship exhausts its missile complement.

Quotes

 * I was aboard the Nelson at Earth. When those two Covie frigates jumped out of Slipspace right in front of use, we let 'em get close, then us and the Hampton Roads opened up with the THUNDERBOLTs. There wasn't much debris left, I tell you!