I can't see any big difference between their uniforms, but I want to be able to know if I'm looking at Marines or Army in photos of soldiers in the Pacific theater. Is there something I'm missing?
Hi, hopefully someone can give you some specific advice, but just fyi, this sub has some links for identifying uniforms/ranks/medals that might help you out https://www.reddit.com/r/AskHistorians/wiki/militaryrecords#wiki_iding_photos_or_uniforms.3A
An important tool that can help is just knowing when and where the photo was taken.
If it was Iwo Jima for instance, or August and September on Guadalcanal than it will 99% be all Marines that were there to photograph.