In World War II, they were able to make an electronic lamp inside the projectile that would not be broken by the acceleration of the shot (20,000 g).

These lamps were used in the remote fuzes.

Their secret was guarded to a similar level as the atom bomb project. They were used only in those situations (air defense) where they could not fall into enemy hands.

Because of them, the chances of shooting down a Fau-1 went from 24% to 79%.

en.wikipedia.org/wiki/Proximit