Crimson Fists
The Crimsons Fists are a second founding chapter of the Imperial Fists. Noted for their crimson gauntlets, which inspired from a ritual with Rogal Dorn and a Imperial Fist successor Chapter Master having a manly handshake with Dorn with cut palms, signifying blood brotherhood between them.
They got fucked over during an Ork invasion on Rynn's World, their home planet, when a stray missile fired from their orbital defense grid struck their own fortress. The damn thing somehow missed its original target, bypassed ALL of the fortress' void shields, and hit the armory directly. The chances of this happening are about as likely as rolling 100 d20s and only getting 1s on all of them.
Note: This was a standard missile fired from an orbiting defensive platform, it normally should have done NOTHING to such a mighty stronghold beyond a small crater. How did something this random happen? We don't know, but Tzeentch probably had something to do with it.
But its okay, because the Crimson Fists still managed to beat the Orks with only two-hundred and twenty-eight marines, 100 of which were killed before an Imperial fleet came to Rynn's World to screw up the Orks, and an unmanned Land Raider that somehow managed to skillfully pilot itself using only its machine spirit and take out a good chunk of the invading Ork horde, including the warboss, before finally being destroyed.
On /tg/
Also known as "Mexican Marines" because their chapter master (Pedro Kantor) has a Spanish first name. (And for the fact that the REAL reason that said Land Raider fucked the Orks' shit up was because it was filled with the remaining 200 battle brothers, and you thought buses in Asia defined carrying capacity.)