In the 1930s, with train tonnage increasing, the Milwaukee began to create three-unit locomotives out of the boxcab units. A simple combination of three was classified EF-2. Twelve EF-2s were assembled, and renumbered 10500–10511ACB. On these, the cab on the center (C) unit was unnecessary and just added weight and length. The center units were therefore shortened by removing the cab, the pilot truck and the frame extension; these were nicknamed "bobtails". These were assembled in between two standard units to create EF-3 sets. These "bobtail" units weighed less than a regular unit. Additional EF-2s were created, but no more were modified into "bobtails".