This is a Kirk-split-by-the-transporter question.The stated question, "Why does the United States need a navy?" and the inferred question, "Why does the United States have the Navy?"I wish I could find the quotable-someone who said that our greatest allies are the Pacific and Atlantic Oceans. Maybe Will Rogers, maybe Benjamin Franklin. It was someone wry, anyway. But we know why we have a navy: the founding fathers foresaw more danger from the sea than from the land and legislated measures to mitigate it. Later, it turned out that more navy was going to help commerce flow. History continued to show how US interests were increasingly extra-territorial, how the Navy helped grease the economic wheels. While WW1 was an iffy justification of global sea power, WW2 was the defining moment for having a world-class, planet-spanning navy. So, we need a navy to protect our shores and protect our trade, that much is pretty clear. But why do we need the Navy, the monstrous fleets that blanket the watery depths with criss-crossing wakes and pointy bits aiming this way and that? Well, we don't. At least not primarily. We could beef up the Coast Guard and develop some pretty impressive area denial weapons and just pay others to protect our shipping when it's out of our range. Why do we have the current US Navy? The rest of the world needs it. After WW1, the US went back into relative isolation. An island unto ourselves, young America didn't want to involve itself with old-world dysfunction. We had plenty of our own, but were too gun-shy to burden ourselves with others' problems, already feeling like 1917-18 was a mistake. After the global devastation of WW2, the US decided that for reasons of self-interest, it was no longer wise to act as if the world's troubles wouldn't also affect America. Many of the other nations around the world, too, mistrusted the US least of the Great Powers, seeing fewer tendencies to empire. As the bi-polar world of the Cold War grew, many other nations allowed the two primary belligerents to act as proxy defenders, keeping the overall armies and navies to a relatively low number. It continues today. The US Navy is specifically requested by many nations to keep a presence in their waters. Treaties define ever-increasing amounts of support from US sea power. The onerous financial strain is starting to tell, however, and we're having to reduce our military interactions across the board. The fear now is that the rest of the world's military spending may rise to fill the perceived gap in US involvement. This hasn't been good in the past and few are enthusiastic about it now. We'll just have to see how things turn out—like we always do.