DC motor applications: Types of fields and benefits of each

For the wide variety of DC motor applications, there are those where a straight shunt motor is preferred and others which seem to require the greater starting torque of a series field. Why are there different field designs and are they interchangeable? What about the nameplates marked “stab shunt” or “str shunt?” The purpose of this article is to clear up lingering confusion about the types of fields as well as the benefits of each.