The Das Kochenhammer is a giant zeppelin manned and guarded by the remnants of the United States Air Force, the Sky Pirates.
Fucking. Everywhere. The Das is quite infamous for flying literally anywhere. The only locations it's locked out of are the Necropolis Gate/El/Heart/Floodplain, Ashen Valley, and Mt. Fisty. It can show up anywhere else, including throughout the bazillion sky tiles that cover nothing but ocean. Your best bet for finding it quickly is someone with Clairvoyance, who can check all the sky tiles very quickly using their speedy .
Fortunately, it moves pretty rarely, so once you get a bead on it its not very hard to track down and board.
Sky Pirates- Sky Pirates are footsoldiers and the basic crew of the aircraft. While having mediocre armor and only wielding assegais, they're organized enough to quickly swarm intruders.
Sky Raiders- There are two of these aboard the Das, both bosses accompanied with a contingent of sky pirates. One wields a luftspeer and the other a sonic scalpel. Killing either will grant you a special weapon as a one-time unique reward. Unfortunately, luftspeers aren't very good, and FlugHammers (from the scalpel raider) are just fully modded Hammerheads which are very easy to acquire, so they're mostly just for looking cool/bragging rights.
Sky Commisar- Appointed as the security officer of the ship is the big bad of the sky pirates boarded on Das Kochenhammer. Wearing endgame armor, and wielding a 12mm with chudstoppers, he offers quite a serious threat to even the most prepared intruders. Some say he even has a special power granted by mutations. He drops an extremely high-value armour as a one-time reward for killing him.
Sky Captain- While not specifically trained for combat, the pilot of the airship can quite well take care of herself as the very last line of defense for her beloved ship. Drops a strong-ish armour that looks really cool upon death as a one-time reward.
Running the Das
The Das requires a little bit of preparation, but so long as everyone in the party knows what they're doing, you'll have no trouble speeding through it with three people. If you're not confident, bring more, it's no big deal. Remember that each boss will only drop their one-time reward for one person in the party, so you may have to return several times to get them all for everyone in the party. The Das respawns 24 real-life hours after it's blown up, so this isn't that hard.
It's hard to give much information about this without spoiling anything. However, it's no secret that you'll need a picker to get into and out of the Das, and that picker will have to be good enough to get through VoxGuard Platinums in a hurry, because there's one on every significant door within the Das. 35/35 locksmith/hack is supposed to be optimal for hack speed. You should also definitely wear bullet armor, because some of the bosses use guns and those don't care about your dodge total.
Lots of players who have hit endgame have also done the Das at least once. There is also a nice little bonus for returning to run it even after you've gotten all the rewards. Ask around, it won't be long until you've found someone who can give you the low-down on the strats for running it. One last chunk of advice: kill the Captain last, be ready to move once you've done the deed, and don't let your picker die.