What does the US Coast Guard do that the Navy and the Marines can’t do?

Question

I’m not from the US and have no military experience either. So the US has apparently 3 maritime branches in the uniformed services and the Coast Guard is, well guarding the coasts of the US. And the other branches can’t do that?

In: Other

Answer 1

First thing is the [Posse Comitatus Act](https://en.wikipedia.org/wiki/Posse_Comitatus_Act).

The federal military is expressly forbidden from acting to enforce domestic policies inside the borders of the United States – which means the Navy and Marines can’t act on civilians within 3 miles of the US coast, at least – so you need a civilian agency to enforce maritime laws in the US.

Hence the Coast Guard.