Quoted:
Kind of a silly poll really. Any serious military thinker understands that the branches have to work together for true effectiveness.
+1
Americans take for granted our ability to conduct joint (inter-service) operations. In many nations, the different branches of their militaries might as well be like foreign countries to one another. There is little communication and cross-training. US joint operations may be clunky and inefficient at times, but we are FAR better at it than any of our potential rivals. Since WWII, our military success is dependent on full spectrum dominance. We need the naval power (Navy) for sea dominance to establish the ability to project power onto foreign shores, we need air power (Air Force/Navy/Marine aviation) to establish air superiority/supremacy so that we can project power over the land, and we need ground power (Army/Marines) to put boots on the ground so as to effectively control territory and effectuate political change. Some of that is redundant, but redundancy is useful in war.
As an aside, the Coast Guard is important because they free up a lot of duties that the Navy would otherwise have to fulfill close to our shores. In recent years, we've even seen the Coast Guard perform some of those duties in foriegn waters (martime security, law enforcement, counterterrorism, etc.).