Readers may not be aware of the difference between a ‘cold launch’ and a ‘hot launch’ when it comes to vertically-launched missiles.
A ‘cold launch’ is when a missile is pushed out of its firing tube or silo by a burst of compressed gas, or an electric mass driver, or some such system other than its own rocket motor. Its motor ignites only after the missile is clear of the tube, sending it on its way to its target. This system has the advantage that no special (and often bulky) exhaust system is needed to guide the rocket exhaust clear of other missiles or components. Russian vertical-launch systems typically use cold launch technology.
A ‘hot launch’ is when the missile’s own rocket motor fires while the missile is still inside its firing tube, launching it and propelling it towards its target. This requires special ducts to direct the rocket exhaust away from other missiles or components, but also removes the need for special gas systems or other technology to launch the missile – it’s essentially self-contained. The US Mk. 41 vertical-launch system uses this technology, which may be viewed in this video clip.
Of course, if the ‘cold launch’ works, but the missile’s rocket motor doesn’t fire, this leaves a missile hanging in mid-air directly above its firing tube – and the vehicle carrying that tube. This can have . . . disconcerting consequences, as the crew of this Russian S-300 long-range anti-aircraft missile system found out the hard way.