ICBMs are commonly launched from below ground. How much fuel could be saved if a missile is launched below ground instead of above? If the tube was deeper with modified launch by a separate chemical launch mechanism to create a back pressure and take to pressure not to destroy the rocket but lift the rocket to achieve much of the velocity to achieve orbit be more efficient? This way rockets of many sizes could use the extra push and may be a reusable first stage launch. 

This piston is powered by rockets that are efficient whilst in compression. 
The lift is created by pressure build up like in internal combustion chamber with a constant burn not from rocketing out.
The maximum Gs up and out.
https://space.stackexchange.com/questions/29521/what-prevents-the-use-of-electric-engines-to-assist-with-spacecraft-launches-l

[![enter image description here][1]][1]
https://metro.co.uk/2018/03/30/russia-tests-4000mph-hypersonic-missile-near-impossible-to-shoot-down-7428694/

[What is the deepest we have ever gone into the Earth?][2]

[![enter image description here][3]][3]

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  [1]: https://i.sstatic.net/NdaBu.gif
  [2]: https://earthscience.stackexchange.com/questions/14168/what-is-the-deepest-we-have-ever-gone-into-the-earth
  [3]: https://i.sstatic.net/xhfPN.jpg
  [4]: https://i.sstatic.net/h4uho.jpg