Loewy-designed body; squared cab windows ("Phase Ib" carbody), GSC trucks: 

   While Fairbanks-Morse was introducing the H16-66, the Chicago & Northwestern approached F-M about building a 6-axle version of the H16-44. The result in 1951 was the H16-66. The carbodies on these early units came with Loewy's styling touches - curved cab windows, slightly sloped ends and raised headlight mounts. In 1952, the carbodies came with squared cab windows. 1953 saw the adoption of a shortened "Trainmaster" carbody.

These later units were commonly called "Baby Trainmasters", while the official F-M description is "1600-HP General Service".