I agree that the 5th fleet is necessary, but only a fraction of our current number of deployed troops are needed for that. And we're definitely not the only country running naval operations in the Indian Ocean.
There is a huge joint effort among countries to protect these routes in the Indian Ocean and up the Red Sea to the Suez.
Combined Task Force 151 - Wikipedia, the free encyclopedia (look at all the different admirals from different countries)
Operation Atalanta - Wikipedia, the free encyclopedia
Operation Ocean Shield - Wikipedia, the free encyclopedia (look at the list of ships)
Believe it or not, the US and Chinese navies are regularly working together to hunt down pirates in the Indian Ocean. So much for being enemies. Yeah, we're providing about 50% of the ships, but clearly we aren't the only players in the game.
This also shows who the REAL threat to the global economy is in the 21st century. Not major world powers, definitely not them. Just poorly trained groups of militants from third world countries. And as we learned in Vietnam, Iraq, and Afghanistan, the solution to fighting third world militants is not to come in with massive armies.