"A small design change could require costly changes in equipment that had already been installed." #readingToday

Although concurrency sped the introduction of new weapons, it also created problems. A small design change in a missile could require costly changes in silo equipment that had already been installed. The prototype of a new airplane could be flight-tested repeatedly to discover its flaws— but a missile could be flown only once. And missiles were expensive, limiting the number of flight tests and the opportunity to learn what could go wrong. A successful launch depended on an intricate mix of human and technological factors. Design errors were often easier to correct than to anticipate. As a result, the reliability of America's early missiles left much to be desired. "Like any machine," General LeMay noted, with understatement, "they don't always work."

Command and Control: Nuclear Weapons, the Damascus Incident, and the Illusion of Safety by Eric Schlosser