This is earnt on the Volga level and is unmissable.
Ranger Hardcore tips
Don't try to fight every mutant in the Terminal. When you climb across the top of the water towers (before seeing the Catfish for the first time) Kill as many as you can without running out of Ammo.
You need to find a level to turn the turntable in the centre with the railcar in it.
Then you'll come to a ladder down in a corner, head down and sprint toward the ladder behind you. Ignoring the enemies. When you get to the top, stick to the wall. the Catfish will attack and kill most of the enemies up there with you. climb the ladder up and follow the walkway in to the opposite corner of the warehouse. Ignoring all Mutants and sprinting passed them.
Head up towards the door. Open it to get a radio signal. Get in the railcar and the trophy unlcoks once outside.