[hoplitis]

I guess that the US "lag" in upgrading "tactical" battlefield weapons/platforms was a result of shifting its attention to "strategic" assets in the post WW2-50s era. No time or funds to improve your armor/antiarmor assets when you've decided that an increased variety and number on nuclear weapons and delivery systems will stabilize or even tip the "balance" to your favor even without actually needing to "press the button". Air-carriers also received attention (succeeding in entering the jet era), strategic submarines, fast interceptors, ballistic missiles etc. The US was "pressing" on the strategic level not the operational/tactical one.