So the U.S. Navy began developing upgrades to Aegis that would enable it to defend against the most widely proliferated ballistic missiles, which were relatively short-range and slow in speed in other words, targets that a system originally developed for dealing with aircraft might be able to address through relatively modest upgrades.
If it chose not to take this draconian step, the Navy would be obliged to slow the rate of production and delivery of the 153 Trident II missiles currently authorized so as to minimize the adverse effects of shutting down the line entirely.