The term “nuclear triad” is a familiar one. It means the three main delivery systems-aircraft, land installations, and naval ones. Or rather, the three main American delivery systems. See, it’s easy to see the grouping of three when you have only deployed three types of strategic platforms: Silos, aircraft, and submarines.

From this American point of view, mobile ICBMs in use by other countries fit into the land part of the triad, and the oft-proposed surface ship bases would fit into the naval part. However, the proposed anchored capsules on the bottom of the sea have more in common with silos than mobile submarines.

So in a different world where nuclear basing was more widespread, the term “Tetrad” or “Pentad” could be used. A tetrad of silos, mobile land missiles (whether via truck, train, hovercraft, or Wienermobile), aircraft, and submarines. Or a pentad of all that plus surface ships.