In terms of Silo (below ground) or Enclosed Missile Systems, the practice of Active Launch (deployment), is broken down into (2) methods. The ''Cold'' and ''Hot'' Launch. Both can be used to deploy ballistic Missiles. However, in the case of Below Ground Launch – The ''Hot'' Launch is most used. ''Cold'' Launches are most often seen with Warships (for safety purposes).
The ''Hot'' Launch Method is performed by a direct ignition of the primary Missile or Rocket Engine. Forward thrust and momentum carry the projectile out of it's launching carrier or Silo upwards until it clears. The projectile then continues on it's ''rise'' to it's altitude or pre-determined trajectory.
The ''Cold'' Launch Method is performed by the addition to external launch packages (mini rocket boosters), which raise the projectile out of it's carrier or silo – to a level where it is deemed ''clear''. The primary Missile Engine or power source then ignites (well clear), sending it along it's way as with The ''Hot'' Launch Method.