The United States Navy said that they could replace NASA the moment they got the mandate, but life, as it often is was not that simple.  Navy rocket ships carried powerful weapons and engines, sheathed in heavy armor, but they were not designed to spend decades away from home, all alone in the night.  Their systems and crews broke down, and many Navy ships limped home on one engine with half their crew sedated.  They were simply not prepared for the mission.