In Civ2 and Civ3, there was a very late game city improvement called SDI (Strategic Defense Initiative) Defense (the second use of the word, "defense," was redundant, but was used in-game, and in '80's and '90's jargon and parlance). This was the formal name of George H.W. Bush (the elder George Bush)'s, "Star Wars program," as it was called in the news at the time, the proposed idea of laser strikes or defense grids from orbiting satellites to, 'zap," ICBM's and SLBM's before they hit a particular friendly city, which never did come to actualization in RL. The improvement, in-game, rendered that particular city immune to nuclear missile strikes (but not spies planting nuclear devices or nuclear power plants melting down).
