One reason the Military Services have trouble operating jointly is that they don't speak the same language. For example, if you told Navy personnel to "secure a building," they would turn off the lights and lock the doors. The Army would occupy the building so no one could enter. Marines would assault the building, capture it, and defend it with suppressive fire and close combat. The Air Force, on the other hand, would take out a three-year lease with an option to buy.
Stolen from Rodger