|Big Boy! Those two words just about say it all when it comes to giant steam power. The twenty-five 4-8-8-4 behemoths constructed for Union Pacific were the mightiest locomotives of the steam era. These still photos are actual scenes ("frame captures") from the Pentrex Union Pacific BIG BOY Collection. All 25 Big Boys are presented in action on the road, as well as in yards, on the Cheyenne turntable, and in servicing areas.