>>7948613>>7948620The three locations are the primary USAF missile wing 'districts', these being:
top left - 341st Missile Wing, Malmstrom AFB, Montana
top right - 91st Missile Wing, Minot AFB, North Dakota
bottom - 90th Missile Wing, F. E. Warren AFB, Wyoming
In the 2000 warhead first strike scenario shown on the map, these 3 bases in particular would be targetted with dozens of nuclear missiles in order to try and prevent/reduce the likelihood of a significant retaliatory counter launch by the U.S. The other black spots on the map are other high priority strategic and key civilian infrastructure/population centre targets in the same first strike scenario.
The 500 warhead scenario also shown on the map is more of a retaliatory counterstrike scenario that would be a possible response to the U.S. launching a first strike against Russian targets, in this case the 3 missile bases likely would have already fired all of their missiles against Russia and so they'd be a lower priority target than American population centres and key civilian infrastructure, especially if the Russians are retaliating with a reduced nuclear arsenal due to the initial U.S. attack..