This page will be a location where I will provide information about articulated locomotives that I have not already covered elsewhere in my site.

I am careful to use the word "articulated" instead of "mallet" to describe these locomotives. Periodically, I hear a Big Boy or Yellowstone referred to as a "Mallet" type locomotive. In my opinion, this is not true. Anatole Mallet designed a steam locomotive with two important characteristings. This locomotive

1. was articulated, and
2. used compound expansion (high and low pressure cylinders)

The Big Boys, Yellowstones, as well as many other articulated steam locomotives, used simple expansion (high pressure cylinders all around), and thus, according to the strictest definition of the term, are not true mallets.

Articulated locomotives such at the N&W Y class did use compound expansion and therefore are true "mallets".