Invaders

Invaders
Number	?
Founding	Unknown
Successors of	Imperial Fists
Successor Chapters	none
Chapter Master	The current one's dead
Primarch	Rogal Dorn
Homeworld	Ogrys (ruined); now Fleet-based Chapter
Strength	Currently 12 Marines
Specialty	Fighting Eldar, Not giving a fuck about casualties
Allegiance	Imperium
Colours	Light Green with gold

The Invaders are a Space Marine background chapter that has picked up notice as Matt Ward likes to add them in his codices. They have the luck of Lamenters with the grit of Crimson Fists, often heading right into the next battle despite having little to no time to replace their losses.

Their biggest accomplishment was destroying Craftworld Idharae. How the hell they did that? Nobody knows (it would seem they simply damaged it beyond repair, later Ward explained it was still recovering from Hive Fleet Naga and lost most of its defences, but since Ward said it, most likely they just are that awesome or performed a Death Star run or something). It also seems that they took an insanely high number of casualties that they still didn't recover from in 43 years (but then again, the Iron Hands STILL haven't recovered from Istvaan V, and it's been 10 fucking thousand years), when Alaitoc showed up with Idharea's survivors at their home world. Only three hundred made it out and they were forced to become fleet based. Of course, with no idea of their recruitment practices but full knowledge of their absolute badassery, it could be their standards are just so high that they have very few potential recruits at any time, drastically slowing their growth in exchange for having significantly superior Marines. It never occurred to the Eldar that the whole reason the Invaders... Invaded was because Idahrae was stupid enough to attack them first. So, once the Invaders chapter has recovered, guess whose next on their shit list? They even were attacked by a xenos species called the "cell-kin". Exactly what it's name implies with a dash of The Flood. They won.

17 years later they lost two full Terminator Squads trying to teleport them down to the Necron World Engine. It's not clear whether they sent both squads at the same time or the second after seeing the first failing.

One year later, they try to liberate a planet that Ahriman took over only to set off a trap that Ahriman made, which resulted in the planet being ripped apart by warp fire. By the time the Grey Knights show up the fix the mess, only 12 of the 300 marines they sent were still alive.

Currently they're fighting Hive Fleet Leviathan thanks to Craftworld Iyanden.

If you're as paranoid as you should be in 40k, you may notice that each time Invaders were fucked up hard after Eldar failed to finish them for good they were fighting the enemies of said Eldar. Connect the dots yourself. Except that the Eldar consistently end up being horribly mauled and their Craftworlds badly damaged or outright destroyed by said Marines. The Eldar manipulate the Imperium to ensure their own survival, they don't manipulate Space Marine chapters into smashing the crap out of the Eldar. The Eldar most likely hope the Hivefleet will finish them off. No doubt other chapters will put two-and-two together and go on a roaring rampage of revenge which will teach the Eldar that, yes, actually, Space Marines really are that powerful.