This drawing of a Sprint Silo was located online. It is not known at this time if the details are accurate or not, probably this is an artistic interpretation. What can be seen is a piston or sabot of sorts, probably used to eject the Sprint at high accelerations. Note the double walled, lenticular cover with what seems like a hollow space. Is this to harden the rocket against a nuclear attack? The dome is obviously the strongest shape to resist pressure, though a cone would probably be better at deflecting heavy impulse impacts. Why hollow? Would this space hold water or other materials for radiation shielding?
** Update **
I now have the source and information about this image. This is an accurate Sprint Silo:
"In the 1970’s, the Martin Marietta Corporation (now Lockheed Martin) in Orlando, Florida, built what is still today one of the most incredible guided missiles ever to fly. The Sprint was a part of the only anti-ballistic missile (ABM) system that the United States ever deployed. Complementing the long-range Spartan interceptor, which was intended to destroy incoming nuclear warheads before they re-entered the atmosphere, Sprint was a short-range screamer with literally split-second reactions. It could intercept any warheads that got past Spartan when they were only seconds from their targets. Ejected from an underground silo by a hot gas generator, the two-stage Sprint accelerated so fast that it would pass a .50-calibre bullet, if fired at the same time, within a second. Atmospheric friction made the outside skin of the second stage hotter than the inside of the rocket motor. It was protected by a thick ablative layer that actually boiled away, carrying the heat with it. Sprint was tested successfully many times at White Sands Missile Range, New Mexico and at the Kwajalein Missile Range in the Pacific. It was beyond-state-of-the-art technology for its day.
This image shows Sprint in its silo. The missile sits on the eject piston, which in turn rests on a ring of springs to cushion the missile from ground shocks. When the gas generator under the piston fires, the piston shoots up the launch tube (stopping when it hits the piston arrestors at the tube mouth) and the Sprint continues out of the cell, literally blasting through the frangible fiberglass, foam and rubber domed cell closure. Tan “wedges” at the missile’s midsection near the second stage fins guide it out the tube. The cutaway shroud near the top of the missile is the “foam sock,” an insulating blanket around the guidance section and warhead that keeps the components at operating temperature at all times."