My entry for @Pilotmario’s Artillery Contest!

In 2265, the solar system is engulfed in a lethal resource war, with the crown jewel of the conflict being the Earth itself. Belligerent and powerful, the Gaia Coalition claims control of the green planet, but it is easier said than done, for threatening forces are just beyond the horizon. The lunar base in which much of the Coalition’s navy is docked has gone dark, and the populations of a terraformed Mars are in active revolt. Beyond the asteroid belt, more radical insurgent groups bide their time and consolidate their strength, preparing for a full-scale military offensive. Amidst the chaos, the Coalition’s Eos Program is born.

The Eos-1 Hydrogen Particle Acceleration System was the first product of the Eos Program, and the Gaia Coalition’s primary means of a defence against long-range orbital bombardment. The primary ammunition was pure hydrogen, which was ionized and accelerated in nine cyclic accelerators. Once the particles reached sufficient speed, they were directed into the primary firing arm, which was a more powerful linear accelerator. The result was a highly concentrated beam that could cut through heavy armor at millions of kilometers away, yet still bypass defensive energy shields.

To generate the destructive power needed for such a weapon, it needed to be huge; the firing arm itself was over 3 kilometers long, and the cyclic generators and their requisite power sources were also extraneously large. Entire bases were built around the weapons, some housing as many as 10,000 people. To conserve space, two towers were built, containing much of the weapon’s population but also containing dedicated hydroponic plants, long-term asset storage, and Coalition command centers, among other things. Due to the extreme importance of the Eos-1 emplacements, the top floors of both towers held flak cannons and anti-armor and anti-missile systems to ward of in-atmosphere attackers. Later iterations of the weapon featured defensive bay doors around the firing arm, to protect from both enemy shelling and the elements.