Thank you so much!!
Did the exemption mean that another son was already serving or served or did this exemption also apply to cases where there was only one able bodied son? For example, if the son was an only child of a widow, could he be drafted or would he be exempt as "One of two sons elected"?
In this particular case, the mother was a widow and there are two sons in the household age 20 and 23. The younger son doesn't appear in the draft registration so it may have appeared to those doing the draft that the older son was the only able bodied son of draft age...