In North America, there is no longer a "Fireman" position on diesels. You have the Engineer and the Conductor in the lead engine, and a "FRED" Flashing Rear End

In North America, there is no longer a "Fireman" position on diesels. You have the Engineer and the Conductor in the lead engine, and a "FRED" Flashing Rear End Device on the rear to control the air brakes, report speed and acceleration back to the head end. More often these days, trains have extra engines on the end (and middle) that are controlled from the front in Distributed Power Units (DPU's). By spreading power out, you have more control, less stress on the couplers, can run a longer train, and the air brakes respond faster (closer to each engine for pressure changes and recharges).