In this diagram from a 1937 issue of Popular Science, the magazine pitched the idea of defensive aerial mind fields, filled with daintily parachuting explosives that would float down to earth for Lord knows who to clean up.

In all seriousness, I do find it kind of quaint that the past imagined the future as some sort of side-scrolling video game. A dieselpunk Gradius, if you will.

[Spotted on Ptak Science Books]