This style marks the departure from the military heel back to the Louis heel. It is clearly not from the earliest part of the century as it lacks the ultra-pointy toe of that era.
You can see what I call the “half apple shape” to the space between where the breast of the heel hits the floor and where the back of the bottom of the vamp ends. As opposed to the “half heart shape” so common both before this era and post-1940s right on up to today’s sort of “half funnel shape”. The negative space formed by the arch had a nice C shape to it.