People who make their living thinking about defense policy and national security like everything to fit into a nice framework, preferably one that can be visualized on a PowerPoint slide. If you are unfortunate enough to be standing next to two officials speaking Pentagonese during a reception, you will note that their language is full of acronyms relating to projects and obscure government agencies—and that they refer regularly to strategic concepts and systems, including the venerable "triad" of nuclear deterrence.

The "triad" concept holds that when a country fields land-, air-, and submarine-based nuclear capabilities, it greatly increases its chances of being able to retaliate after an attack. In the case of the U.S. and the Soviet Union during the Cold War, for example, if either side would have launched a first strike and knocked out the other side's land- or air-based systems, submarines would still have provided a devastating second-strike capability. Nuclear war was such an awful prospect that it long was described as intrinsically the ultimate universal deterrent, rendering an actual armed conflict between NATO and the Warsaw Pact that might escalate unthinkable.