The DDA40X is a 6,600 hp (4.92 MW) D-D diesel-electric built by the General Motors EMD division of La Grange, Illinois for the Union Pacific Railroad. Nicknamed "Centennial" and "Big Jack", the DDA40X uses two diesel engines on two SD-40 carbodys (each 3,300 hp (2.46 MW)) and is the most powerful single-unit diesel locomotive ever built, although more recent locomotive designs such as the GE AC6000CW and EMD SD90MAC have come close. It is the second most powerful locomotive ever built, losing to the Union Pacific GTEL. It is also the longest single-unit diesel locomotive ever built.