While orbital bombardment is a concept that the Covenant have refined to a precise science, humanity is much newer to the form of warfare. Concieved in the early 20th Century, during the Cold War, the original Project: THOR was intended as a way to circumvent the Outer Space Treaty forbidding the placement of Weapons of Mass Destruction in space - technically, possessing no unconventional payload, a THOR projectile is simply a rod of tungsten carbide or depleted uranium, neither of which has provisions in any treaty. Much of the theory was refined in the 20th and 21st Centuries, but it would not be until the 23rd Century that the first weapon systems would see deployment in limited numbers, during the Interplanetary War. They became more common during the Insurrection, and by the end of the Human-Covenant War had become standard on most frigates and cruisers, allowing them to provide orbital bombardment capability, though nothing like the scale of Covenant systems.
Kinetic bombardment is by no means a new concept. The earliest proposals by science fiction writers called for the crashing of nearby satellites, asteroids or meteoroids, which would have produced devastating, if unrefined, results - thankfully, then, it was the military industrial complex that took the idea and ran with it, producing the much more refined Project THOR concept. Originated by Jerry Pournelle and developed by Boeing in the 1950's, the idea was that a solid tungsten "telephone pole" be kept in a geosynchronous orbit above the Earth, using thrust vectoring rockets to maintain a stable position. When needed, this projectile would enter the Earth's atmosphere, using stabilising fins and its thrust vectoring systemt for course correction and stability, striking a target with infinitely more accuracy than a meteorite. Such an impact would be vary in equivalency - the smaller projectiles would be equivalent to only a 500 lb "conventional" bomb, and larger projectiles would have proportionately larger yeilds, but a fraction of the cost.
Even more attractive to the defence industry, the projectile would be extremely difficult to detect, possessing an high closing velocity and small radar cross section. Better still, the infra-red launch signature occurs in orbit, with no fixed position, and is only a fraction of, for example, a ballistic missile. Smaller projectiles could be kept in "carrier" satellites in significant numbers, allowing multiple strikes within a rapid frame of time, resupplied by rocket or shuttle launch. The only apparent drawback would be that the weapon's sensors would become blind during reentry, obscured by the plasma sheath, so a mobile target would be difficult to hit, especially if it deviates from its expected course mid-entry.
Naturally, there was considerable interest in developing a weapon of this type. Founded in 2089, recent newcomer to the defence market Sierra Space Systems had made their name with the development of efficient VASIMR thrusters for manned and unmanned space exploration probes, first used in the colonisation of Mars. For their next success, CEO Janus Adelig turned to a property with decidedly more militaristic applications - Project THOR. Their first deployment, the KKV-X1, was launched in 2102 via the Japanese Tanegashima Space Center and placed in a geosynchronous orbit - the first test fire occurred at its Alice Springs testing centre, with a tungsten-carbide projectile impacting successfully on its target, a nearby abandoned town purchased by Sierra for the demonstration. The timing and success were crucial - the KKV-X1 was essentially just the projectile itself, a single-use disposable weapon that, if wasted now, would badly damage Sierra's reputation. Observed by representatives of various national military organisations, especially the Peoples Republic of China and the United States, Sierra secured contracts from a dozen nations for KKV-1A satellites. Investigations were conducted on whether it could be converted into a material delivery system, but these would be abandoned in 2089.
Later models, such as the KKV-2 and KKV-7C, would be reusable multiple-launch platforms for the kinetic kill vehicles, housing up to two dozen projectiles, each able to be manoeuvred independently to strike multiple targets. During the Caucasus Wars, Russia would deploy its KKV satellites in anger for the first time, but it would not be the only user - smaller nations such as Georgia, while lacking launch sites for their own satellites, had purchased satellites already orbiting, and retaliated in kind. When the nations reformed into the Federated States of the Caucasus for a united front against Russia, it possessed two dozen of the satellites, a significant threat to Russian territories in the region. United Nations intervention in 2112 stopped the majority of the damage, but the effectiveness of the KKV had certainly been proven - it is always telling that the most effective weapon systems do their job so well that they fall into disuse, killing becoming too easy, and the KKV satellites would remain orbiting but inactive for another fifty years.
When war had broken out on the Jovian moons, the German and UN forces stationed there had been forced to rely on dropship and gunship support - these were fallible, as the Frieden had proved, susceptible to Sufrace-to-Air Missiles. When the Frieden and Koslovics began their Earth campaign, sparking the Rainforest Wars, they discovered that the orbital defence infrastructure possessed no such vulnerability. Attempts at using electromagnetic pulse weapons had some success, but the sheer number of satellites meant that the Frieden and Koslovics never enjoyed the security of the Earth-based forces. With the need for an orbital defence grid established, Sierra and a number of other defence companies were contracted to design a replacement for its last satellite, the forty two year-old KKV-18BII - the result was the THOR-1. The first of a new generation of kinetic kill behicle launch platforms, the THOR used a small but efficient coilgun to launch a smaller projectile at greater velocities - the result was a superior weapon in all regards, with a significantly smaller radar cross sections and infra-red launch signatures, higher kinetic energy and closing velocity, and more accurate than any past KKV weapons. Though expense limited their production, with the largest purchase orders placed by the US, Russia and China, the THOR series would affectionately become known as "Thor's Hammers," after the ancient lightning god Thor, and in 2168 Sierra officially adopted the name "Mjolnir THOR-2" for its second-generation satellites.
Small brushfire conflicts would continue to be fought on Earth and among the Sol colonies, but never on quite the same scale as the Interplanetary Wars - the Mjolnir satellites would continue to play a major role, though, used to destroy confirmed hostile bases of operations, terrorist training camps, mobile transports, and so on. Unified Earth proposals to automate the Solar Defence System in 2311 were popular, but the UNSC's reluctance to remove the human element from warfare continued to see the Mjolnir satellites play only a supporting role, rather than being the primary reactionary means. In hindsight, this was perhaps a narrow escape - the spread of THOR satellites may have been percieved by the UE Parliament as replacements for colonial police forces, but such heavy-handed responses used so frequently wuld almost certainly have incited dissent far quicker.
The ushering in of the Great Age of Colonisation came with many drawbacks for Sierra - while it had made a fortune out of its mass-production of the SSX-12A Shaw-Fujikawa Translight Engine (2342 Update), newly established colonies had shown no interest in purchasing orbital defence satellites such as the THOR. Even among the various solar system colonies, the satellites had already begun to be retired. With the spread of colonial peace, the concept of orbiting kinetic bombardment satellites had become obsolete - other contractors began to discontinue their manufacturing of such weapons, moving on to more profitable enterprises, such as colonial ship construction or terraforming. Sierra would be slower to follow, but the last THOR satellite to leave its Ganymede production facilities was delivered to Mars in 2393.
When tensions began to flare up among the Outer Colonies in the 2400's, Sierra saw the return of a niche market for the THOR. Marketing it as a "colonial security deterrent system," the THOR-32A began production in 2486, with a dozen purchased by the Reach Colonial Parliament and established in geocynchronous orbit above the colony. When the Insurrection broke out into full war, these THOR satellites would prove instrumental in the limiting of terrorist damage, though counters would be found, and vulnerabilities exploited - Insurrectionist training camps would be camouflaged, both optically and thermally, and frequently relocated, making them difficult to pinpoint from orbit. Worse still, a number of satellites fell under Insurrectionist control, either as a direct result of CMA sympathisers or through electronic hacking of Reach Colonial Defence Grid assets - the bombing of Kadajh in 2495 would be a political disaster, denting confidence in the CMA's ability to protect the civilian population. When the UNSC became entangled in the Insurrection, it immediately set about securing these satellites, installing state-of-the-art security software and limited AI defences, finally locking all Insurrectionists out of the system.
Seeing the effectiveness of orbital-launched kinetic kill vehicles in insurgent suppression, the UNSC began tentative investigations of installing a small THOR package on an interstellar warship - the first such ship to feature the weapon would be the UNSC Aeneas, a converted colonial support ship/carrier, would would prove instrumental in suppressing Insurrectionist forces on a dozen colony worlds. The ability for a warship to carry THOR capability with it would open up new avenues in offensive warfare - a MAC was simply too powerful to use against a planetary target, and missiles were slow, easy to detect, and expensive. The success of the Aeneas' THOR weapon system would spread through the fleet, and THOR-equipped ships would become popular among UNSC Marine and Army ground forces, re-adopting the "Thor's Hammer" nickname.
The attack of the Covenant against Harvest would see the full mobilisation of the UNSC for the first time since the Interplanetary Wars, with all available military forces converging on Harvest for its recapture. The half-decade long ground campaign, what would become known as the "Five Years of Hell," would see the THOR used on a far more frequent basis than during the Insurrection - THOR-equipped ships would become a strategic neccessity in the fight for control of Harvest's surface, providing orbital fire support against Covenant infantry and armour forces, command centres, artillery batteries, and surface-deployed warships. The number of THOR systems in use among the Navy would still be extremely small - far too small to handle the need for them. Though effective when used, the limited numbers would see them marginalised during the Harvest campaign, to the irritation of both naval and surface combatants.
Afterwards, during the UNSC's massive mobilisation, rearmament and recruitment campaign, ship designs would be introduced into surface that featured the THOR as standard. Future frigates and cruisers, which have traditionally supported ground forces from orbit, would feature THOR launch platforms as part of their design, the tungsten carbide/depleted uranium rounds manufactured to be compatible with a standard Magnetic Accelerator Cannon - ships like the UNSC Spirit of Fire would be able to alternate rounds, allowing some interchangability of roles between the THOR and MAC. In the fight for the Outer Colonies, THOR-equipped ships would see action at a hundred worlds as UNSC Marine, Army and Air Force personnel held off the Covenant to allow the civilian colonists to evacuate, serving as extreme long range artillery support. In some cases, THOR strikes would be deemed neccessary for the destruction of sensitive material in the enforcement of the Cole Protocol.
Naturally, the THOR's use did not go unchallenged by the Covenant. The development of deployable energy shields over sensitive areas may have been a direct response to the UNSC's use of THOR systems - while they were certainly effective at protecting their contents from orbital strike, though, they also made their most important infrastructure obvious to any outside observer, and UNSC ground forces would target these areas for assault first, an effective strategy. In the space campaign, Covenant ship captains would pinpoint and target UNSC ships that looked likely to carry THOR systems, denying their use to ground forces - the launch requirements, needing a stable orbit facing the underside of the ship towards the planet, made them relatively easy to discern and target. UNSC carrier groups would assign fighter defences to protect THOR ships from Seraph fighters and boarding craft, but there is little that can be done against, say, a plasma torpedo or energy projector beam.
By the end of the war, most of the UNSC's THOR-capable ships had been wiped out by selective Covenant destruction, with less than a dozen existing when Reach fell. When the Covenant finally moved against Earth, the UNSC Aeneas, the first, was also the last of its kind, and would be lost during the Battle of Ares IV. During the subsequent Post-War Reconstruction efforts, as part of the UNSC Navy's rearmament programs, all ships would possess energy shield capability, a radical change from past ship design, one that was revolutionary - such protective measures for orbital fire support ships meant that they were far less vulnerable, and able to be used in vital tactical roles. The War of Vengeance would see the emergence of a dedicated ship class, the Aeneas-class Arsenal Ship, completely AI controlled and designed to provide indirect fire support to ground forces. Though it certainly differed from other Arsenal Ships of the time, such as the Invincible and Retribution-class, it would prove effective at its role, and would free up other classes for conventional space warfare, an increasingly important need as the Blood Covenant and Privateer Alliance engaged UNSC naval forces.
Although Sierra Space Systems had collapsed into economic bankruptcy in 2549, after most of its Outer Colony support base had been destroyed, it had been acquired by Misriah Armouries, a Mars-based defence contractor, and many of its designs were also acquired by Misriah. From 2549 onwards, Misriah would become the primary producer of THOR systems for UNSC and colonial security use, beginning with the introduction of the THOR-44C/UU, and THOR systems would again become a standard armament aboard ships designed to support ground forces, such as frigates and support ships, with the first of the modern systems equipped on the UNSC Ajax.
- "I remember back on Arcadia, we had what looked like a division of Grunts storming Alpha Base - next thing we know, something slams right in amongst them, wipes most of 'em out in...what, seven? Seven hits. We were on burial detail for the enemy that day!"
- "The name is right! When you see these things hit, they feel like the lightning god himself has taken it upon himself to smite your foes!"
- "I still don't see why every ship doesn't use them. It would sure as hell make us ground-pounders happy!"
- "A THOR may make the groundpounders happy, but its useless in ship-to-ship combat, which is where the UNSC is really losing this war. Forget the ground - if we can't hold the space above a planet, the people down below are screwed either way."
- "Early THOR systems required specialised projectiles. The newest version is interchangable with the standard MAC shell. Just another example of Navy streamlining - I'm not complaining, if it means it can be more common or effective."