The Explorator Fleets are fleets sent by the Adeptus Mechanicus to explore less-known parts of the galaxy. Think of them as Rogue Traders, add in ship loads of tech priests, ancient space-faring technologies (which the priests keep to themselves, the selfish little...) and a big old focus on finding hidden technological secrets rather than booty and spoils and you have yourselves an Explorator fleet.
Their primary mission is to find lost technology, especially a working STC system (though printouts are also welcome). Often, they find other things, like new worlds and civilizations, or worlds with which contact had been lost centuries before, or Forge Worlds founded by a previous expedition. Often they find danger, which is why they bring along a detachment of Skitarii, just in case. The drive to find working STCs fill the tech-priests with the sort of (balls-to-the-walls, batshit fucking insane) fervor that makes them risk huge fleets and massive resources in order to even get a whiff of them.
Explorator Fleets tend to be crewed by the most curious of tech-priests, which means that when they find ancient tombs filled with impossibly advanced technology, they generally poke around a little too hard and a little too deep (ancient tombs being a colloquial slang for the orifices of your mother), which wakes up the inhabitants. With said inhabitants being cantankerous old robots with no time for kids ruining their lawn, this often lead to lots of deaths (this happens in at least two of the Ciaphas Cain stories). It's a seriously endemic problem, probably compounded by the fact that some tech-priests worship the Necrons as angels of the Omnissiah.
The reason why the Adeptus Mechanicus isn't too keen on sending out Explorator Fleets is because they are worried about all of those nasty corrupting influences out there in space, ya know. The lure of forbidden technology, the sight of tech heresies, xenos technology....it can all turn a tech-priest on their little metal head, and at times not in the way the higher ups would like. Their reverence for technology means anything unusual (even a long lost type of electric toaster) can make them giddy and excited and since they are far away from the steadying hands of the senior Techpriests Magos of the forge worlds (where they can monitor them "Big Brother" style) the chances of heresy are pretty darn high. Add the fact that exploratory fleets usually include the most open minded of tech-priests and well....such things are self evident. This does mean that some of the best useful and inventive work is done by Explorator Fleets (although the Rogue Trader books do insist that some tech-heresies like accepting Xenos tech or widespread genetic manipulation are banned and must be kept secret - although they tend to happen anyway).
So why allow such high risks? Why not allow the Rogue Traders or Imperial exploration fleets to bring back technologies, letting them do the hard work? The answer is greed (and also Grimdark or whatever). The Adeptus Mechanicus are the biggest hoarders in the universe and are worse magpies than the Blood Ravens. They keep all the best technology for themselves and only really share the mass produced stuff (and only because of their ancient agreements or because almost everything the Imperium gets from the AdMech it is also building without the AdMech and so the Mechanicus pretends to “share” what the Imperium already has)). While the imperial navy has to manually load torpedoes by hand with hundreds of workers, the Mechanicus have auto-loaders on their ships. While the Imperial Guard are armed with flashlights and carboard vests, their Skitarii counterparts are pimped to the fucking gills with the best equipment. This is made worse by each Forge World being technically their own domain and often keeping secrets from their fellows simply because they can and they tend to not be near each other, making direct contact difficult if not impossible (it also sucks to spend twenty years trying to get to another, far-off Forge World to find it Nommed or blown up).
The worst thing is that the tech-priests don't actually know how the tech works; on the (rare) occasion when they do manage to get their greasy mechadendrites on it (relying, as they do, on instruction manuals even less technically detailed than the 'Dummy's Guide to...." series). So if an Explorator Fleet did find some unusual tech the Imperium at large would probably not know about it for a thousand years because between drawn out religious ceremonies, their desire to keep secrets
(cause fuck the Emprah and all his sheep, the Omnissiah is where it's at), HERESY!*BLAM* and just having no idea what button to press, it would take that long for the tech-priests to make any damn good on it. Admittedly, this is better than them pushing the wrong button and opening a new Eye of Terror. Its not like rushing out technology has ever gone horribly for all those involved. In a way this goes back to why the Mechanicus has Explorators: the Imperium is not afraid to experiment and use the scientific method. These things are heresy to the Mechanicus even though it usually works.
On the plus side Explorator Fleets offer good settings for Warhammer 40k role-playing games. Want to be a tech-priest and his retinue of slightly colourful nutters exploring a new corner of the dark universe? Well now you can! It's only a matter of time though before one of them stumbles on a dimensional rift and find a borg cube or something.....("All hail our brothers in bionics! Wait, you want to do what? Well I can't join your collective I am already part of a priesthood....wait, wait what noooooooooooooooo. Oh you are injecting more machines into me? All hail our brothers in bionics....").
Known Ship Hulls
- Lathe-class Monitor-Cruiser; An Adeptus Mechanicus Light Cruiser designed around deep space exploration and extreme self-reliance. These ships, when properly outfitted, can operate for decades without returning to imperial space for resupply. These would make up the bulk of Explorator fleets.
- Secutor-class Monitor-Cruiser; An Adeptus Mechanicus Light Cruiser designed to excel at the art of war. Tougher than all of the other Light Cruisers and yet still more mobile than true Cruisers. Due to being designed from the ground up to be a Warship, this Light Cruiser is fitted with Cruiser sized Void Shield Generators.