[jp10]

Biplane opposition during Japanese military operations in the 1930's China were not uncommon and the concept of massed Infantry fire against them would be better than nothing. More of a left over concept from WW1 than anything else.
In the 1980's the U.S. Army still had Infantry training drills on how to engage low flying A/C with rifle fire and that included jets. They just didn't bother with a fancy sight thingy.