Dense Pack is a strategy for basing intercontinental ballistic missiles (ICBMs) for the purpose of maximizing their survivability in case of a surprise nuclear first strike on their silos conducted by a hostile foreign power.
The strategy was developed under the Reagan administration as a means of safeguarding America's inventory of MX missiles during the final decade of the Cold War.
This concept relies entirely on the warheads approaching from a certain direction, and as the Soviets introduced their Fractional Orbital Bombardment System and high-angle "lofted" trajectories, this no longer offered any extra protection.
In 1979, after a long debate on the topic, President Jimmy Carter selected the "multiple protective shelters" concept for basing the MX.
When Ronald Reagan took over in 1981 he agreed to reexamine the basing question, as opposition by Nevada senator Paul Laxalt had become overwhelming by this point.
For the immediate future, 60 MXs would be placed in surplus Titan II missile silos while a final basing solution was chosen.
First, the advent of multiple independently targetable reentry vehicles, or MIRV, negated the concept due to their ability to conduct a time-on-target barrage.
Finally, Dense Pack was perceived by some to be a provocative, if not overtly hostile measure at a time when nuclear warfare seemed to be a distinct possibility.