The notion of a missile silo seems self-evident now, but the US military got the idea from the British Blue Streak missile project:
The missiles used liquid oxygen and kerosene propellants. Whilst the vehicle could be left fully laden with 20+ tonnes of kerosene, the 60 tonnes of liquid oxygen had to be loaded immediately before launch or icing became a problem. Due to this, fuelling the rocket took 4.5 minutes, which would have made it useless as a rapid response to an attack. The missile was vulnerable to a pre-emptive strike, launched without warning or in the absence of any heightening of tension sufficient to warrant readying the missile. To negate this problem DeHavilland created a stand-by feature. A missile could be held at 30 seconds’ notice to launch for ten hours. As the missiles were to be deployed in pairs and it took ten hours for one missile to be prepared for stand-by, one of the two missiles could always be ready for rapid launch.
To protect the missiles against a pre-emptive strike while being fuelled, the idea of siting the missiles in underground silos was developed. These would have been designed to withstand a one megaton blast at a distance of half a mile (800 m) and were a British innovation, subsequently exported to the US.