With the election of Donald Trump and his Dec. 22 tweet calling for the United States to “greatly strengthen and expand its nuclear capability,” advocates of additional nuclear reductions saw their chances of furthering the disarmament agenda go up in smoke. However, they are now doubling down on efforts to eliminate the intercontinental ballistic missile (ICBM) leg of the triad, arguing that the aging Minuteman III should not be replaced.

Their hopes were pinned to Trump’s defense secretary, James Mattis, who last year offered this testimony on Capitol Hill: “The nuclear stockpile must be tended to and fundamental questions must be asked and answered: We must clearly establish the role of our nuclear weapons: do they serve solely to deter nuclear war? If so we should say so, and the resulting clarity will help to determine the number we need. Is it time to reduce the triad to a diad, removing the land‐based missiles? This would reduce the false alarm danger.” (Emphasis the author’s.)

In asking whether the United States should move to a diad, critics of the nuclear triad are both misreading Gen. Mattis and underappreciating the role ICBMs play in strategic stability. By questioning the utility of the triad, he is doing what good military leaders have always done: challenging assumptions. Reading his earlier testimony as a full-throated endorsement of eliminating the ICBM is a mistake. Rather, it should be understood within the context of a thoughtful general officer asking a penetrating question to which he is open to a compelling answer. It is through this process of “iron sharpening iron” that the military ultimately reaches the best possible, although imperfect, solution. Indeed, at his Jan. 12 confirmation hearing, Gen. Mattis declared his support for the Ground Based Strategic Deterrent program and articulated some of the reasons ICBMs are valuable.

Having had the opportunity to stand before many a general officer and answer penetrating questions, my response to Gen. Mattis’ specific query would be rather straightforward. The probability of a false alarm leading to miscalculation is at an all-time low. With the U.S. Air Force operating both space and land-based detection and early warning systems and the requirement for verification of any launch through the process of dual phenomenology (space detection followed by land-based radar verification), the statistical probability that the United States would launch ICBMs as a result of a false alarm is close to zero.

Russia is also replacing its Oko-1 space-based missile attack warning system (MAWS) with a new and advanced early warning system that will more closely approach the capabilities of the United States. The Russians are also replacing older systems with the Voronezh-M and Voronezh-DM long-range over-the-horizon land-based radars.

While furthest behind, China is also deploying a space-based network of early detection satellites to complement its over-the-horizon radars. When complete, it will be a modern and capable early warning system, backed by the world's densest land-based over-the-horizon radar network.

These systems, which are fielded by the three countries that possess ICBMs, make the prospects of a false alarm leading to an exchange of nuclear weapons more remote than ever. This was not the case four decades ago when tensions were at their highest. Today, when the United States and Russia have the smallest number of operationally deployed strategic nuclear weapons since the early 1950s, the need to field advanced land-based ICBMs is at an all-time high for several reasons.

First, American ICBM fields create a requirement for an adversary to strike over 450 discrete targets—in the U.S. homeland—with more than 900 of their own ICBMs in order to destroy the U.S. ICBM force. This requirement drives adversaries to a more risk-averse position because of the inherent uncertainty in achieving the desired destruction and the certain response that will follow. Given that ICBMs are the only leg of the triad that must be destroyed by a nuclear strike, it should come as no surprise this causes such risk aversion.

Second, Russia and China are dramatically improving their air and missile defenses. Russia, for example, is developing—and potentially exporting—advanced integrated air defenses like the S-500, which reduces the probability of success for the bomber leg of the triad and may have the ability to hit incoming reentry bodies. China is focusing on the development of anti-submarine warfare capabilities, which will one day make the Pacific transparent and put American ballistic missile submarines at risk.

Third, at an estimated cost of $60 billion to $80 billion over the next three decades—ten percent of the military’s total planned modernization expenditure—development and fielding of GBSD is an absolute bargain and will offer the greatest return on investment of any modernization effort.

In time, the Air Force will undoubtedly make the case to Gen. Mattis for the ICBM — and a compelling case it will be.