Looking ahead is always daunting; crystal balls are not what they once were. If you were looking 20-odd years ahead in, say, 1975, when the Soviets seemed to be doing rather well in the Cold War, would you have imagined that the Soviet Union itself was not long for the world? On the other hand, you probably would have understood the potential for technology.

The two big developments were better command and control through more powerful computers, and stealth. The most important U.S. Navy systems of the early 1990s were already embryonic in 1975. You might even have noticed that a lot of the technology around you seemed to be improving more and more slowly. In some way, once the easy quick steps had been taken, it took longer and longer for a great deal of technological effort to make a visible difference.

We have a Navy for three reasons. One is that we want to deal with threats as far from the United States as possible. Only a navy can stay in place near foreign shores, on a sustained basis, without local permission. Our crystal ball is unlikely to tell us what problems we will face in 2030, but we certainly expect to remain a world power, and world powers always face foreign problems. This first reason is sometimes called presence (for deterrence), and sometimes power projection (when deterrence does not work). Ballistic-missile submarines exemplify presence. The most recent form of power projection has been the war in Afghanistan. In case that does not seem very naval, remember that without the fleet in the Arabian Sea, we would not have been able to fight in Afghanistan in the first place when we got there in 2003.

The second reason is that we badly want to maintain world prosperity, because the less prosperous people are, the more likely they are to fight – and as the richest country in the world, we are target No. 1. The central fact of sea power has always been that it is much easier to move anything heavy from one place to another by sea rather than on land. The classic accounts of sea power are really about the fight to control world trade by sea. Even when there was not so much world trade, the basic fact of sea power is why it was possible to mount seaborne invasions during World War II, or for that matter, why a major air base can move across the sea at 30 knots. In the past, along with the value of trade was the immense value of world fisheries, which keep many people from starving. For some decades, we have been taking more and more of our resources from the sea, too. Those resources, such as undersea oil and gas, have to be guarded.

A third reason is the direct defense of the United States. More than a century ago, the United States chose forward defense over local defense, the coast defense mission declining sharply. If for some reason forward defense became impossible, coast defense would revive. As it is, in an age of terrorism, we are more and more concerned with the possibility that our enemies will use large merchant ships to attack us, just as they used airliners on 9/11. Right now that it mostly a Coast Guard problem, but it involves the Navy’s efforts at ocean surveillance (to pick out suspicious merchant ships long before they get to the United States).

Coast or local defense does have one growing naval component. Right now the most successful component of U.S. ballistic-missile defense seems to be the Aegis system on board destroyers and cruisers. That is partly due to the sophistication of the system, but also due to the ability to place systems where they are most effective, out to sea in the direction of a threat. It seems that more and more Third World countries are working on long-range ballistic missiles. To these countries, missiles are, among other things, a way to turn off unwanted U.S. power projection. Many of the governments involved see the United States as a fundamentally hostile force in the world (the Iranians put this idea most forcefully, but they are not alone).

It seems unlikely that the world of 2030 will be enormously more peaceful than the world of 2012. In that case, sea-based ballistic-missile defense may be a lot more important. The need for such defense will change the balance among U.S. naval missions – and resources. We are already feeling a fiscal pinch. In the past, fiscal problems have often made for innovation – as in the growth of the carrier between World War I and World War II. The time scale to 2030 is much the same as that between the two world wars.

It seems unlikely that these missions will change either in character or in priority over the next 20 years. The cracks in the crystal ball show when we ask a bit more. Will we be facing a single major enemy capable of contesting sea control, or will we still be dealing with local problems overseas (plus, say, terrorists)?

Another way to look ahead is to ask how sea power itself may change. Maybe the best way to do so is to look at the basic facts of life on which sea power is based. The most basic is that, as stated previously, it is a lot easier to move heavy weights by sea than by land. Hence the explosive growth of shipping as the world economy increasingly goes global. Now the sea is a more and more important source of resources; maybe the reason we’ll still be burning gasoline in 2030 will be a lot of deep-water oil wells. Both factors say that navies will be more, not less, important in 2030. Whatever the threats, they will have to defend a lot of activity on the surface of the ocean.