The following is the Feb. 2, 2023, Congressional Research Service report, Defense Primer: Strategic Nuclear Forces.
From the report
The Nuclear Triad
Since the early 1960s, the United States has maintained a “triad” of strategic nuclear delivery vehicles. These include long-range land-based intercontinental ballistic missiles (ICBMs), long-range submarine-launched ballistic missiles (SLBMs), and long-range heavy bombers equipped to carry nuclear-armed cruise missiles and gravity bombs. The number...
https://news.usni.org/2023/02/08/defense-primer-u-s-strategic-nuclear-forces