The advance of missile and rocket technology in the late 1950s started to change the strategic picture; the significance of Sputnik (launched in 1957) was always that if the USSR could orbit a small satellite around the Earth, they could do the same with a nuclear weapon. By 1959, both the USA and the USSR had mounted nuclear warheads on intercontinental ballistic missiles (ICBMs), fulfilling Brodie’s prophecy that nuclear weapons would accelerate the development of longer-range and harder to intercept platforms: now the platforms had effectively infinite range and were effectively impossible to intercept.

This also meant that a devastating nuclear “first strike” could now be delivered before an opponent would know it was coming, or at least on extremely short notice. A nuclear power could no longer count on having enough warning to get its nuclear weapons off before the enemy’s nuclear strike had arrived. Bernard Brodie grappled with these problems in Strategy in the Missile Age (1959) but let’s focus on a different theorist, Albert Wohlstetter, also with the RAND Corporation, who wrote The Delicate Balance of Terror (1958) the year prior.

Wohlstetter argued that deterrence was not assured, but was in fact fragile: any development which allowed one party to break the other’s nuclear strike capability (e.g. the ability to deliver your strike so powerfully that the enemy’s retaliation was impossible) would encourage that power to strike in the window of vulnerability. Wohstetter, writing in the post-Sputnik shock, saw the likelihood that the USSR’s momentary advantage in missile technology would create such a moment of vulnerability for the United States.

Like Brodie, Wohlstetter concluded that the only way to avoid being the victim of a nuclear first strike (that having the enemy hit you with their nukes) was being able to credibly deliver a second strike. This is an important distinction that is often misunderstood; there is a tendency to read these theorists (Dr. Strangelove does this to a degree and influences public perception on this point) as planning for a “winnable” nuclear war (and some did, just not these fellows here), but indeed the point is quite the opposite: they assume nuclear war is fundamentally unwinnable and to be avoided, but that the only way to avoid it successfully is through deterrence and deterrence can only be maintained if the second strike (that is, your retaliation after your opponent’s nuclear weapons have already gone off) can be assured. Consequently, planning for nuclear war is the only way to avoid nuclear war – a point we’ll come back to.

Wohlstetter identifies six hurdles that must be overcome in order to provide a durable, credible second strike system – and remember, it is the perception of the system, not its reality that matters (though reality may be the best way to create perception). Such systems need to be stable in peacetime (and Wohlstetter notes that stability is both in the sense of being able to work in the event after a period of peace, but also such that they do not cause unintended escalation; he thus warns against, for instance, just keeping lots of nuclear-armed bombers in the air all of the time), they must be able to survive the enemy’s initial nuclear strikes, it must be possible to decide to retaliate and communicate that to the units with the nuclear weapons, then they must be able to reach enemy territory, then they have to penetrate enemy defenses, and finally they have to be powerful enough to guarantee that whatever fraction do penetrate those defenses are powerful enough to inflict irrecoverable damage.

You can think of these hurdles as a series of filters. You start a conflict with a certain number of systems and then each hurdle filters some of them out. Some may not work in the event, some may be destroyed by the enemy attack, some may be out of communication, some may be intercepted by enemy defenses. You need enough at the end to do so much damage that it would never be worth it to sustain such damage.

This is the logic behind the otherwise preposterously large nuclear arsenals of the United States and the Russian Federation (inherited from the USSR). In order to sustain your nuclear deterrent, you need more weapons than you would need in the event because you are planning for scenarios in which some large number of weapons are lost in the enemy’s first strike. At the same time, as you overbuild nuclear weapons to counter this, you both look more like you are planning a first strike and your opponent has to estimate that a larger portion of their nuclear arsenal may be destroyed in that (theoretical) first strike, which means they too need more missiles.

What I want to note about this logic is that it neatly explains why nuclear disarmament is so hard: nuclear weapons are, in a deterrence scenario, both necessary and useless. Necessary, because your nuclear arsenal is the only thing which can deter an enemy with nuclear weapons, but that very deterrence renders the weapons useless in the sense that you are trying to avoid any scenario in which you use them. If one side unilaterally disarmed, nuclear weapons would suddenly become useful – if only one side has them, well, they are the “absolute” weapon, able to make up for essentially any deficiency in conventional strength – and once useful, they would be used. Humanity has never once developed a useful weapon they would not use in extremis; and war is the land of in extremis.

Thus the absurd-sounding conclusion to fairly solid chain of logic: to avoid the use of nuclear weapons, you have to build so many nuclear weapons that it is impossible for a nuclear-armed opponent to destroy them all in a first strike, ensuring your second-strike lands. You build extra missiles for the purpose of not having to fire them.

(I should note here that these concerns were not the only things driving the US and USSR’s buildup of nuclear weapons. Often politics and a lack of clear information contributed as well. In the 1960s, US fears of a “missile gap” – which were unfounded and which many of the politicians pushing them knew were unfounded – were used to push for more investment in the US’s nuclear arsenal despite the United States already having at that time a stronger position in terms of nuclear weapons. In the 1970s and 1980s, the push for the development of precision guidance systems – partly driven by inter-agency rivalry in the USA and not designed to make a first strike possible – played a role in the massive Soviet nuclear buildup in that period; the USSR feared that precision systems might be designed for a “counter-force” first strike (that is a first strike targeting Soviet nuclear weapons themselves) and so built up to try to have enough missiles to ensure survivable second strike capability. This buildup, driven by concerns beyond even deterrence did lead to absurdities: when the SIOP (“Single Integrated Operational Plan”) for a nuclear war was assessed by General George Lee Butler in 1991, he declared it, “the single most absurd and irresponsible document I had ever reviewed in my life”. Having more warheads than targets had lead to the assignment of absurd amounts of nuclear firepower on increasingly trivial targets.)

All of this theory eventually filtered into American policy making in the form of “mutually assured destruction” (initially phrased as “assured destruction” by Secretary of Defense Robert McNamara in 1964). The idea here was, as we have laid out, that US nuclear forces would be designed to withstand a first nuclear strike still able to launch a retaliatory second strike of such scale that the attacker would be utterly destroyed; by doing so it was hoped that one would avoid nuclear war in general. Because different kinds of systems would have different survivability capabilities, it also led to procurement focused on a nuclear “triad” with nuclear systems split between land-based ICBMs in hardened silos, forward-deployed long-range bombers operating from bases in Europe and nuclear-armed missiles launched from submarines which could lurk off an enemy coast undetected. The idea here is that with a triad it would be impossible for an enemy to assure themselves that they could neutralize all of these systems, which assures the second strike, which assures the destruction, which deters the nuclear war you don’t want to have in the first place.

It is worth noting that while the United States and the USSR both developed such a nuclear triad, other nuclear powers have often seen this sort of secure, absolute second-strike capability as not being essential to create deterrence. The People’s Republic of China, for instance, has generally focused their resources on a fewer number of systems, confident that even with a smaller number of bombs, the risk of any of them striking an enemy city (typically an American city) would be enough to deter an enemy. As I’ve heard it phrased informally by one western observer, a strategy of, “one bomb and we’ll be sure to get it to L.A.” though of course that requires more than one bomb and one doubts the PRC phrases their doctrine so glibly (note that China is, in theory committed to developing a triad, they just haven’t bothered to actually really do so).

Bret Devereaux, “Collections: Nuclear Deterrence 101”, A Collection of Unmitigated Pedantry, 2022-03-11.