A prototype locomotive for study and research purposes was built in the middle of 1925. A second was built in 1929. They were totally different machines in just about every way except the boxcab type carbody.
The first production-type locomotive intended to be duplicated was built in late 1936 -- although, in fact, it was not duplicated. However, it was the first unit to be built with the VO engine, which would remain in production for another ten years in varying degrees of modification. From that point, Baldwin was effectively in the diesel business.
The last unit, a model S-12 switcher, was built in the first days of August 1956. The company itself remained independent (in other business lines) until 1965, when Armour bought it out. However, in 1970, Greyhound, who had bought Armour, liquidated all remaining assets of Baldwin-Lima-Hamilton. In 1971, what was left, directly, of the replacement parts business was bought by Innovest and became known as the Baldwin-Hamilton Company.
But, as far as serious production of diesel locomotives goes, the dates are 1936-1956.