Visor caps and garrison caps were regulation issue for both officers and enlisted. The Warrant Officer's badge is shown (and it caused some resentment amongst Flight Officers), the Officer's badge is a large spread eagle, while the enlisted badge is a small eagle on a large disc. There are differences in the material and details of construction, but that is the easy way to tell in photos, especially black and white.
All ranks wore the garrison cap (cunt cap, envelope, schiffchen etc). Officers hats were piped with black and silver, or black and gold braid, while enlisted personnel had optional piping in branch of service colour. This was added after the fact, or on private purchase (PX) hats.
Withe massive build up of the US Army, general issue of the visor cap to enlisted personnel ceased - along with a number of cloth saving changes to the dress uniform. The garrison cap was cheaper to make, and easier to store, and easier in general to deal with, as it could be tucked into the belt upon entering a building, instead of tucked under the arm.
Officers, who expected to purchase their own uniforms, were given greater baggage and living spaces, continued to favor the visor cap for it's 'officeriness'
