Elanus 51cm L/100 Pattern 2660 Naval Gun

The Elanus 51cm L/100 Pattern 2660 is a Mass Accelerator Cannon designed and built by the Turian Elanus Corporations installed on the refitted and the later production variant of the Federation John A Warden-class Battlecruisers and subsequently, Terran-constructed battleships and battlecruisers of domestic designs. The Terran licensed variant is designated as 'M2660 20  Naval Gun. '''The gun is also used by the Federation Army as planetary surface defense guns and orbital defense platforms during the Batarian War.

Description
One of the best dreadnought mass accelerator ever built by the Terrans, the gun is known for its reliability and accuracy. The original design was patterned by the Turian's Elanus Starship Engineering of Elanus Risks Control Services Corporation and early Turian built specimens are first used to arm the post-Third Bug War refitted and newly constructed variant of the John A Warden-class battlecruisers.

The M2660 is a relatively fast loading MAC, compared to other Dreadnought Spinal Cannons of its era. It is capable of delivering a two-shots salvo for every 20 seconds with its twin-linked fire control mechanism. The M2660 is 100 meters in length and can be loaded with two types of ammunitions. A high velocity polycrystalline tungsten slug with muzzle velocity of 3500 km/s (1% fraction of lightspeed) and an Anti-ship Nuclear Super Heavy Slug which contains pure nuclear fusion warheads to maximum of 40 kilotons blast.The SHS only has the muzzle velocity of 3250 km/s but have a higher bursting output as it was specifically designed for damaging the internal structures of enemy starships through kinetic blasts with its delayed fuse.

Performance wise, the gun is very effective at penetrating the shields and armor of the thin-skin converted Batarian Hegemony's Dreadnoughts and Fast Battleships at mid-range (25,000 km) but less effective against the better armored slow moving dreadnoughts of Turian and Asari origins. The Anti-ship Nuclear Slug offered better penetration against armored modules but at a cost of shorter effective range (15,000km) while the Tunsten Slug gave it a superior long range shield piercing capability at the cost of relatively poor armor piercing performance.

M2660 Mark I
The M2660 Mark 1 is a Mass Accelerator of Turian design adopted by the T.F.S.F for fixed installations on the refitted John A Warden class Battlecruisers and for flexible orbital defense turret. The fixed dreadnought spinal installation was developed first, as a dreadnought gun mounted in the bow of the ship, the size of the gun however present an egronomic problem, so the newly refitted John A Warden class required a significant modifications such as removal of 8 high density laser batteries, with only four remaining as well as the additional space required to install the autoloader of the gun. The auto loader have a magazine capacity of 10 shells loaded prior to firing, usually loaded with either Anti-Ship Nuclear Slug or Shield-Disruptor High Velocity Tungsten Slug with 90 rounds ammunition stowage for each battery.

The installation of the gun to the John A Warden required a significant modification of the vessel by having an elongated sensor mast at the "bottom" deck module of the ship which carried the sensor modules and fire control systems of the ships due to the large space required in the hull to mount the cannon and its auto-loader. The flexible turret mounted variant was built with an inverted feed mechanism to solve the weight problem and reducing recoil while firing, ammunition capacity for the autoloader also improved, with extra 20 slugs storage for a total number of 120 rounds per battery. The larger size of the flexible version proved to be impractical for installation on smaller Terran Dreadnought designs so the Mark II variant is developed to mitigate this problem.

M2660 Mark II
The limited ammunition capacity of the MK I model proved to be a big disadvantage in combat. Even when the gun can be equipped with a 20 rounds autoloader, the ergonomic issue is still a problem as the bigger magazine size cannot fit their more compact Dreadnought designs. The Terrans adopted a more practical solution by developing the MK II model which have shortened barrel and an improved gun calibrator for syncing with the ship fire control system as well as a larger capacity autoloader with 30 shells can be pre-loaded in the magazine. The barrel length of the gun is also extended by 50m.

The M2660 MK II is fitted on the newer Terran Dreadnought designs such as the Amagi-class Battlecruiser and the Admiral-class Fast Battleship as well as a supplementary armaments for the Yamato, one of the Izumo-class Super Dreadnought alongside its Hyper Electron Laser Accelerator Cannon.