“A soldier is one who fights as part of an organized land-based armed force;[1] if that force is for hire the person is generally termed a mercenary soldier, or mercenary.[2] The majority of cognates of the word “soldier” that exist in other languages have a meaning that embraces both commissioned and non-commissioned officers in national land forces.”
When ashore, Marines fight that way, but they aren't and will never be 'soldiers'. They are an amphibious force. US soldiers are part of the US Army.
The majority of cognates of the word “soldier” that exist in other languages
I suspect other 'marines' would object to being classified as soldiers as well, in any language.