The Navy specializes in blowing things up. They do not have have the know how or the equipment.
Another example of this was Desert Storm. The military brought in oil drilling and capping experts to extinguish the fires left behind by Hussein in Kuwait after the invasion there. They did not have the equipment or knowledge to do it themselves even in the "simpler" case of above-ground oil leaks/fires.
The fact is we were not prepared--not BP, not any government agency to handle this type of disaster. I suppose we all hope and assume that the folks making the decisions to create the potential for disaster also build appropriate safety measures and have the right equipment to respond--but we'd be wrong. On a positive note, we are poised to gain the experience and wisdom to prevent such a thing from happening in the future. If we (citizens, government, etc) perform adequate due diligence, we will hopefully prevent companies like BP from charging ahead thinking first of the bottom line and second of the environment and the rest of us.