I took a good close look at this photo (as close as I could considering the poor resolution). The white shirts were out before Pearl Harbor with the Class As for officers, and the Sam Brown belt was out by 1942. The hat is a 1930s design, and it sure looks to me like the branch insignia is sewn on after being embroidered onto a patch on the collars. The cut of the jacket is more like the post-WW1 redesign of the Class A jacket when the collar was opened up and a tie added. That, and the tent behind him, would strongly indicate to me that this photo could easily have been taken in the early 1930s to sometime around 1940. Certainly pre-WW2, no doubt in my mind, as I've been collecting US WW2 stuff for almost 20 years now and is my primary hobby.