Cloud seeding was used as a weapon in Vietnam.
Yes, it was....dubbed
"Operation Orange": colloquially...seems it had another "code-name:...."Agent Orange".
TWO factors or 'elements' in that plan. ONE was defoliation, as explained below...another was the fact that in that region of the World it was possible to "seed" clouds in attempt to induce heavy precipitation....which would mean RAIN (not snow...too warm for snow). To induce an impediment to the so-called "enemy" (the North Vietnamese.) ...and to impede their ability to operate ground vehicles.
Back then? This was (now deemed illegal) an attempt to use defoliants and herbicides, to destroy jungle foliage, and thus remove the "cover" that the (then "enemy") used to evade detection.
In any event, notwithstanding the concept, and any sense of "whether or not it was Legal??" at that period of time....(or even if it was "ethical"??).
These sorts of 'sprays' were conducted at VERY low altitudes.
NOTHING at all to do with the more "modern" meme of so-called "chem"trails. (Although this is often brought up in the context of the so-called "chem"trail "debate", unfortunately, and inaccurately).