The choice is obvious: United States Marines Corps (USMC). Perhaps in conjunction with the U.S. Navy (of which they are a component).
The Marines are an agile force, designed to respond and rapidly adapt to a variety of situations. Hence their small size, compared to other branches of US military. But they can pretty much do it all. Although a longer campaign would obviously require support from other US branches.
But note I refer to US outfits. That is all I know. Not much knowledge of non-US forces.
So, based on that, I would say maybe a hybrid USMC/Navy type thing.
Perhaps you could consult with someone with some military experience?
Disclosure: My dad was a career Marine and several uncles served shorter stints in the Marines--except one who was in the Navy. I have had/have relatives in the Army. So I am perhaps just a tiny bit prejudiced.

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