Question: The company which is  a subsidary of the American footwear company founded by Charles Beckman is a principal supplier of what. 
Sentence (from "S. B. Foot Tanning Company"): The company also supplies over 1.5 million linear feet of leather for use in the production of military footwear per year, extending a tradition that began with World War I, when the tannery supplied boot leathers for the construction of soldier boots.
Relevant evidence: No