Here is some Wikipedia info on W&S that mentions how the Duplex brand fit in. Still says nothing about the forklifts. Found one site that suggested the forklifts were based on a Ford tractor, but I don't know.
Construction equipment[edit]
A Gradall XL5100-III excavator, formerly a product of Warner & Swasey.
In 1946 Warner & Swasey Company acquired the patent rights to manufacture the Gradall telescopic boom excavator from the brothers Ray and Koop Ferwerda with their manufacturing company, the FWF Corporation, of Beachwood, Ohio. The Gradall, a type of hydraulic machinery, became a business of the new owner as the Gradall Division with operations in Cleveland. In the year 1946, the Gradall was the first production hydraulic excavator that was designed and manufactured in the United States. In July 1950, Gradall manufacturing operations were moved to New Philadelphia, Ohio, where it continues, in 2017, as Gradall Industries, Inc., a global manufacturer of telescopic boom excavators and industrial maintenance machinery. Gradall Industries, Inc. is a business unit of the Alamo Group of Seguin, Texas. [16]
The foundation of the Warner & Swasey Construction Equipment Division with five product lines was started in 1946 with the development of the first production hydraulic excavator; the GRADALL®. This machine was new technology for the industry and was highly versatile and productive for a variety of work. The DUPLEX TRUCK® Company of Lansing, Michigan, a heavy duty and specialized truck manufacturer was acquired in 1955 to supply truck chassis for the GRADALL and future Warner & Swasey backhoe excavator and crane products. In 1957 the Company sought a broader market penetration into the hydraulic excavator market. It acquired the Badger Machine Company of Winona, Minnesota, with its six HOPTO® hydraulic excavator models which complimented the Gradall models. The Company acquired in 1967, the Sargent Engineering Corporation of Fort Dodge, Iowa, a manufacturer of hydraulic cranes. Their six SARGENT HYDRA-TOWER® CRANE models enabled the company to move into another large segment of the construction industry using hydraulic machinery. That same year the Company partnered with a Canadian paper industry association in the manufacture of the ARBOMATIK® a line of hydraulic tree harvesting equipment. Through corporate diversity into hydraulic construction equipment, the growing popularity and productivity of this type of hydraulic machinery yielded strong business growth for the Warner & Swasey company of Cleveland, Ohio during the years of 1946 through 1977.