Raum-Kampfjet Mark V (Introduced as RK5) is a Dahl gunship, operated by the Lost Legion to protect the vault on Elpis. It is equipped with multiple rocket pods and shock turrets, and will occasionally drop nukes.
While fighting the Vault Hunters, the pilot will spurt out insults.
The Beginning of the End
Vault Hunters sighted! OPEN FIRE! (Mission only)
"I've had it up to here with you Vault Hunters."
We fight until the last of us falls! (Mission only)
"Yeah, DIE, DIE, DIE."
Don't let up!
"Eat lasery death"
"Are you ready for a missile massacre?"
I'm retreating -- cover fire, NOW!
"Charlie, Foxtrot, I'm outta here cover me."
I've had about enough -- you guys pound on 'em for a while!
"To the last!"
Stop your belly-aching and love the bomb!
This is it!
RK5 is a re-spawning boss after the mission is completed, and has an increased chance to drop The Sham.
RK5's critical hit locations are the Missile Pods, the Cockpit, and the Engine.
"Raum-Kampfjet" means "space combat jet [aircraft]" in German.
A ship similar to the RK5 appears first during a cut-scene in Eye to Eye. It deploys Zarpedon's Mech to the arena and drops a couple of Lost Legion Soldiers before it leaves.
Two Dahl crafts sharing RK5's model appear in The Dawn of New Pandora. They do not attack and are ranked 10 levels above the player, but can be shot down.
Multiple copies of this Gunship can be seen at Outfall Pumping Station. They are static and only serve as game scenery.
This implies that RK5 is the name of a specific type of spacecraft instead of a single, unique aircraft.