US security does not require nearly 1,600 nuclear weapons deployed on a triad of systems—bombers, land-based intercontinental ballistic missiles (ICBMs), and submarine-launched ballistic missiles (SLBMs)—to deliver them. A smaller arsenal deployed entirely on submarines would save roughly $20 billion annually while deterring attacks on the United States and its allies. A missile dyad is more politically feasible but saves less.
The triad grew from the military services' competition to meet the Soviet threat. The arguments for it arrived to rationalize its components. The public rationale was a second strike: a diversity of delivery systems insured the nuclear arsenal's survival against a Soviet preemptive attack. The more sophisticated rationale was a first strike: deterring Soviet aggression against European allies required the ability to preemptively destroy their nuclear forces.
Once competition between the Navy and Air Force diminished in the 1960s, they stopped denigrating each other's nuclear delivery systems and began arguing for the triad's necessity. That agreement prevented appreciation of the flaws in its justifications. The survivability argument exaggerated Soviet capability to threaten U.S. forces. The first-strike argument overlooked the accuracy gains allowing various weapons to destroy Soviet nuclear forces. And keeping the Soviet army out of Western Europe was never that hard; it did not require the ability to disarm their nuclear deterrent.
U.S. power today makes the case for the triad more dubious. Survivability is no longer a feasible justification. No U.S. adversary has the capability to destroy all U.S. ballistic submarines, let alone all three legs, and there would be time to adjust if that changed. Nuclear weapons are essentially irrelevant in actual U.S. wars, which are against insurgents and weak states without nuclear arsenals. Nuclear threats have a bigger role in hypothetical U.S. wars with nuclear-armed powers. But cases where the success of deterrence hinges on the U.S. capability to destroy enemy nuclear forces are far-fetched. In any case, U.S. submarines and conventional forces can destroy those forces. Even hawkish policies do not require a triad.
Nuclear weapons are no longer central to the identity or budget of the Air Force and Navy. Especially while austerity heightens competition for Pentagon resources, service leaders may see nuclear missions as red-headed step-children that take from true sons. That shift would facilitate major reductions in the nuclear arsenal, the elimination of at least one leg of the triad, and substantial savings.