Hard to define this nice sounding phrase. Wasn't the U.S. Navy created in order to keep trade routes open and protect U.S. private sector commerce? Did the "survival of our nation absolutely depend on it"? Some would say absolutely yes and some might say not necessasrily.
Well, interesting that you chose the USN for your example, because basically the mission of the Navy is to be a blue water one: to be deployed not just overseas, but on the high seas.
I'm talking Air Forces bases overseas. Army bases overseas. Engaging in "limited" armed conflicts or "peace keeping missions." Etc.