Promotion of the missile gap had several unintended consequences. The R-7 requires as much as 20 hours to be readied for launch so they could be easily attacked by bombers before they could strike. That demanded them be based in secret locations to prevent a pre-emptive strike on them. As Corona could find the sites no matter where they were located, the Soviets decided not to build large numbers of R-7s and preferred more-advanced missiles that could be launched more quickly.