Ever since the Cold War, we have depended on all three legs of this triad as part of our nuclear deterrence. Each had advantages and disadvantages. Submarines could be hidden and could therefore survive a first strike, but until recently they were also the least accurate. Land-base ICBM's were the most accurate, but they were only useful as a deterrent if we launched on warning (since we would have only 30 minutes or so from the launch of an enemy missile before it hit the silo. Finally, unlike missiles that could not be stopped once launched, bombers had the advantage that they could be withdrawn before they attack.
The challenge now facing the country is that we will soon need to update and modernize all three legs of the triad, and we are potentially facing a huge trillion bill to maintain the current to maintain the Nuclear Triad. The current ICBMs were first deployed in the 1970's and will soon need to be replaced by the Ground-based Strategic Deterrent. The current submarine fleet is also old and will be replaced by the new Columbia-class submarine. Finally, the nuclear-armed bomber fleet is older than the pilots who fly them, and will be replaced by the B-21 Long Range Strike Bomber.
A trillion dollars is a lot of money so there are some (including former Defense Secretary William Perry) who argue that it is time to retire the land-based ICBM, and rely solely on submarines and bombers for our deterrence once the current ICBMs become obsolete around 2030. The argument is that submarines and bombers have developed nearly the same accuracy as the ICBM, that because ICBMs must be launched on warning, they are likely to lead to disastrous errors, and that bombers and submarines alone can provide a deterrent. Here is how Secretary Perry explains why the ICBM should be scrapped:
First and foremost, the United States can safely phase out its land-based intercontinental ballistic missile (ICBM) force, a key facet of Cold War nuclear policy. Retiring the ICBMs would save considerable costs, but it isn’t only budgets that would benefit. These missiles are some of the most dangerous weapons in the world. They could even trigger an accidental nuclear war.
If our sensors indicate that enemy missiles are en route to the United States, the president would have to consider launching ICBMs before the enemy missiles could destroy them; once they are launched, they cannot be recalled. The president would have less than 30 minutes to make that terrible decision. This is not an academic concern.
While the probability of an accidental launch is low, human and machine errors do occur. I experienced a false alarm nearly 40 years ago, when I was under secretary of defense for research and engineering.This sounds pretty persuasive. So what is the contrary view? Supporters of the Nuclear Triad point out that removing ICBMs makes the targeting decision easier for our opponents. There are only three bases for our bombers and two bases for our submarines, while a challenge to our ICBMs requires an attack on all many silos. In addition, supporters of the current triad note that ICBMs are no longer as destabilizing as Perry suggest. Tom Nichols and Dana Struckman of the Naval War College explain:
Perry makes a fair point that the accuracy of both the bomber and submarine force is on par with its land-based counterpart. But this, in turn, means that if America were to “ride out” a strike on the ICBM force, the submarines and bombers—as Perry admits—could do whatever tasks are left once the enemy has emptied its own ICBM force at us. The major virtue of the ICBM force, then, is not what it can do after an attack, but that that the enemy will have to take it into account before an attack, and consider the cost of starting an all-out nuclear exchange between the homelands.
Moreover, if the ICBM force were targeted, the United States would still be able to attack, with great speed and precision, not only the remaining enemy strategic force but important parts of enemy military infrastructure. Russia or China would then be the ones to face the fateful decision to attack cities, a situation they will inevitably bring on themselves the moment they initiate the conflict—which is exactly the realization that should deter them in the first place.
So what is the right answer? A trillion dollars is still a boat load of money. As Nichols and Struckman point out, while the ICBM serves a strategic purpose, we don't need as many ICBMs as we do now to deter an attack. In addition, if we negotiate further cuts in our nuclear arsenal with Russia (and perhaps China), we can further reduce the costs of our nuclear deterrence while still have the strategic parity needed to deter an attack.