Don Stauffer wrote:

I have seen lots of pictures of people painting cars in factories in the
pre-WW1 time period, using paint brushes. I then realized I have no
idea when spray painting was invented. Anyone know? They certainly had
air compressors by then.

The original description was air brush rather than spray gun and they
were in existence well before 1900.
There's plenty on the net about the subject.
Devilbiss existed pre WWI.

Tom