Those who love steam engines are no doubt familiar with the Challenger, the fastest freight locomotive of the Union Pacific fleet in the 1940s and 1950s.

The Challenger, based on the design for a successful freight engine, was the largest, heaviest and most powerful articulated passenger locomotive ever built. The powerful engine and 67-inch-diameter driving wheels enabled it to both negotiate the steep grades of the passes through the Rocky Mountains and achieve speeds necessary for express passenger service. - TS