The Guardian Fleet was the name of the military force of the Solar Consortium for most of its history from the defeat of the Kretonians in 2806 to the destruction of Earth in 3002. The Guardian Fleet made use of large numbers of Specialists designed to serve as rank-and-file soldiers, although its officers were all normal humans. While it can trace its origins to surviving units of the original Vanguard of the Stellar Consortium after the Kretonian Invasion in 2651, it bore little similarity to that storied orgainization. The Guardian Fleet had a reputation for brutality and extreme xenophobia, a reputation enhanced by some of its most prominent commanders, including Colin Neidermeyer.
The Guardian Fleet commanded a sizeable military force on Earth and Mars, and acted to contain and keep pressure on the Free Luna Protectorate on Luna. The Guardian Fleet maintained several Gunstar satelites in Earth orbit, and many of its training and specialist-breeding facilities were located on Mars.
The Guardian Fleet was briefly re-named the Human Defense Force, or HDF, by megalomaniacal Consortium President Yosef in the year 3000. However, this name change was ignored by nearly everyone outside Yosef's hearing, and after he was replaced the name was officially changed back to Guardian Fleet. For a brief time, it was somewhat fashionable to combine the names, and the force was referred to as the HDF/Guardian Fleet.
The Fleet was dramatically weakened during the rebellion of Mars against the Consortium, and nearly half its strength joined the rebellion, forming the basis of what would become the Martian Legions, the military force of the Martian Republic. The Guardian Fleet declined sharply in power and influence after that, and when Earth was plasma-bombed, some of the surviving units (Including the flagship, the GFS Resistance) were absorbed by the Martian Legions, while others escaped and operated for a while as terrorists or pirates around Sol System.
The Guardian Fleet reappeared as a powerful military force during the Moebius Effect crisis, as the Alternate Earth had a very different history in which the Fleet was stronger and more aggressive than it had been in this universe, apparently to combat a continued Kretonian presence in that universe. However, the assault of the Nall Fleet in the wake of the Moebius Effect weakened and dispersed much of the alternate Guardian Fleet, and many of its units were destroyed by the second plasma-bombing of Earth. It remains possible that some elements of the Guardian Fleet escaped the reversal of the Moebius Effect and remained in this universe, but on balance as an organization it has ceased to exist.