Between 1931 and 1940 ALCO built 177 high hood (HH) switching locomotives of various horsepower ratings and body styles. The “HH” models were forerunners to the popular S-series of switchers which featured lower hoods. ALCO’s high hood switchers were in production long before similar models from competitors EMC/EMD (1935) and Baldwin (1937). Interestingly, the “HH” model designation is a term coined by rail historians to describe what ALCO documentation had simply referred to as 600-hp or 660-hp switchers. In later years ALCO had referred to these early units as “high hood switchers” so this designation is appropriate.