  The Yang-Mills field strength incorporating a non-Abelian feature is one of
the cornerstones of the standard model. Although Yang-Mills gauge theories have
been around for over fifty years, surprisingly the derivation of the Yang-Mills
field strength using classical gauge theory does not appear anywhere in the
literature. In their 1954 paper, Yang and Mills had to invent a non-Abelian
field strength to satisfy certain criteria. In Section 5 we use Yang's gauge
transformation in a heuristic derivation of the Yang-Mills field strength. The
preceding sections cover material relating to the derivation. Section 3 shows
where Pauli in the article cited by Yang and Mills gives an expression for the
electro-magnetic field strength in terms of a commutator. For some reason, Yang
and Mills did not use this approach.
